TM 11-5895-217-35D E P A R T M E N T O F T H E A R M Y T E C H N I C A L M A N U A L

FIELD AND DEPOT MAINTENANCE MANUAL

TRANSPONDER SET AN/APX-44

This copy is a reprint which includes current

pages from Changes 1 through 3 and 5through 7.

H E A D Q U A R T E R S , D E P A R T M E N T O F T H E A R M Y

J U L Y 1 9 6 0AGO 10004A

W A R N I N G

DANGEROUS VOLTAGES EXIST IN THIS EQUIPMENT

Be careful when working on the 125-volt and the 300-volt plate and power supply circuits,or on the 150-volt bias supply circuit.

DON’T TAKE CHANCES

EXTREMELY DANGEROUS VOLTAGES (600-volt dc and 1,200-volt dc)EXIST IN RADAR RECEIVER-TRANSMITTER RT-494/APX-44

CAUTION!

Do not make resistance measurements on the transistorized circuits ofRadar Receiver-Transmitter RT-494/APX-44.

(See paragraph 72 before making resistance measurements on these circuits.)

Changes in force: C 1, C 2, C 3, C 5, C 6, and C 7

TM 11-5895-217-35C 7

CHANGE HEADQUARTERSDEPARTMENT OF THE ARMY

No. 7 W A S H I N G T O N , D.C., 2 May 1968

DS, GS, and Depot Maintenance Manual Including Repair Parts ListTRANSPONDER SETS AN/APX-44 AND AN/APX-44B

TM 11-5895-217-35, 27 July 1960, is changed as follows: The manual now also applies to:

Nomenclature Order No. Serial No.Transponder Set AN/APX-44B FR28-043-P6-22095 (E) 501 through 999

FR28-043-P6-22795 (E) 1 through 1042

Note. The parenthetical references to a previouschange (example: “page 3 of C 3“) indicates pertinentmaterial was published in that change.

After the paragraph heading, add “(for Equip-ments Without SLS Capability)” in the follow-ing places:

Page 76, paragraph 55.Page 77, paragraph 56.Page 81, paragraph 57.Page 100, paragraph 64.

Page 2, chapter 1, below the title, note (page1 of C 5). Add after the second sentence:For AN/APX-44 modified by modificationwork orders MWO 11-5895-217-30/3 and forAN/APX-44B procured on Order FR 28-043-P6-22095 (E), serial numbers 1 through 500modified by modification work orders MWO11-5895-217-30/3, Order FR 28-043-P6-22095 (E), serial numbers 501 through 999,and Order FR 28-043-P6-27795 (E), serialnumbers 1 through 1042, the AN/APX-44Bcontains a sidelobe-suppression ( SLS) circuit;the video amplified card has been replaced bya VIDEO AMPLIFIER/SLS card. All illus-trations and text pertaining to the video am-plifier card do not apply to the VIDEO AM-PLIFIER/SLS card. Page 11, paragraph 16 (page 2 of C 2). Addafter subparagraph e:

f. Transponder sets that contain sidelobe-suppression (SLS) circuitry reply to three-pulse, SLS-type interrogations. The additional

pulse is a control pulse that is inserted in afixed position after the first pulse of a mode-determining, two-pulse interrogation to permitmore positive control of transponder responseswhen operating in close proximity to the radarground station. The three-pulse SLS systemreduces ground station antenna sidelobe trig-gering of undesirable transponder replies.

Page 12, paragraph 18b. Make the followingchanges.

Add after subparagraph b (5):(6) Sidelobe-suppression control pulse-

risetime 0.2 µsec or less, decay time 0.4µsec or less, width 0.7 to 1.2µsec, with separation of 2 µsec ± 0.15for all interrogation modes.

After subparagraph c, add new subpara-graph d.

d. The three-pulse, sidelobe-suppression typeinterrogation system uses an added pulse,designated P2, for transponder control. Aradar ground station transmits this pulse at afixed separation from the first interrogationpulse but at an amplitude considerably lowerthan that of the interrogation first pulse (P1)and last pulse (P3). Sidelobe control pulseP2 is transmitted omnidirectionally around theground station with an amplitude that exceedsthat of my sidelobe being radiated by the radarantenna and is able to initiate transponder setcontrol before the radar antenna sidelobescan cause erratic replies.

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Page15, section II, below the title, add:

Note. All references to interrogation pulse pairsare applicable to equipments with SLS capability un-less otherwise specified. The SLS control pulse maybe present in the receiver and video output duringthree-pulse SLS interrogations, but is not pertinent tothe discussion unless specifically mentioned.

Page 18, paragraph 25e. Make the followingchanges:

After subparagraph e, add:e. 1. Refer to figure 8.2, receiver-transmitter

with SLS, block diagram, for the followingdiscussion. Spike suppressor V303 eliminatespulses of 0.3 µsec or less in width and decreasesthe width of each interrogation pulse by 0.3µsec to eliminate most of the received noisepulses. Sidelobe blocking oscillator V301 re-ceives interrogation pulses from V303 and isadjusted to produce output pulses that are ap-proximately 0.6 µsec in width while maintain-ing the original interrogation pulse separation.The reshaped interrogation pulses from V301are applied to all three decoders (V351, V352and V353). When one of the decoders receivesa correct code and mode, main gate multi-vibrator V404 is triggered. Passage of theSLS control pulse (P2) to the video ampli-fier/SLS card input is possible only when pulseP2 has an amplitude sufficient to overcome IFsuppressors CR204 through CR207 (d above).Pulse P2 must have an amplitude that exceedsthe 10-dbm threshold of the IF suppressorcircuit at the 2.0-µsec separation point to befed to spike suppressor V303 for triggeringof V301. Decoders V351, V352, and V353 willreject the P2 pulse if there is a lack of pulse-pair coincidence. Pulses P1 and P2 from V301are combined and made additive when properlyspaced. This action produces a single pulseof sufficient amplitude to trigger sidelobemultivibrator V302. The 35-µsec output pulseproduced by V302 is used to blank V301, sup-

pressing P3, and to prevent decoding of pulseP3. It is also rectified by automatic overloadcontrol (AOC) rectifier CR308 to reduce ifamplifier (V202, V203 and V204) sensitivitywhen the preset prf has been exceeded.

Page 19, paragraph 25f. After subparagraph(3), add:

(3.1) For equipments with SLS, the nega-

Page

tive main gate pulse from V404 isamplified by main gate amplifierV454A and is applied to suppressorcathode follower and inverter ampli-fier V304 (fig. 8.2). The output ofV304 cuts off sidelobe blocking oscil-lator V301 for the duration of themain gate and prevents interrogationof the transponder during the cutoffperiod. Amplifier V304 also suppliesthe main gate suppression pulse toSUPPR jack J106 and to main gateAOC rectifier CR305, where the gateis rectified and is applied as bias toIF amplifiers V202, V203, and V204when the preset prf rate is exceeded.This governs receiver sensitivity bythe interrogation repetition rate, andprevents the excessive transmitterduty cycle that would result if thetransponder set replied to all inter-rogations.

29, paragraph 27f (6). Add the follow-ing note after subparagraph (6).

Note. SLS control pulse P2 falls at the 2.0- secinterval and is blocked in the if. suppressor circuitunless pulse P2 has sufficient amplitude to exceed the10-dbm threshold of the IF suppressor. A 9-dbm grayarea exists for passage of P2 due to IF suppressorcircuit and interrogation signal characteristics. PulseP2 must pass the IF suppressor whenever P2 is equalto or greater in amplitude than pulse P1.

Page 31, paragraph 28, heading. Add afterthe heading: (Without SLS).

2

Figure 19.1.

figure 19

figure 18

Figure 18.1.

Page 32.

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3

figure 20

Figure 20.1.

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Page 33. Make the following changes:Afte figure 21, add figure 21.1.

Figure 21.1. Sidelobe multivibrator (SLS), partial schematic diagram.

Add after paragraph 28:28.1. Video Amplifier Card (With SLS)

(fig. 18.1)a. General. The input interrogations to the

video amplifier/SLS card are positive inpolarity and 0.7 µsec wide. Spike suppressorV303 eliminates all received pulses that are0.3 µsec wide or less. The output of V303 con-sists of positive pulses approximately 0.4µsec wide that are fed to blocking oscillatorV301. Two additional inputs are fed to V301;a sidelobe-suppression gate pulse, which blanksV301 and prevents pulse P3 from reachingthe decoders and a main gate suppressionpulse, which blanks V301 and prevents addi-tional interrogations from overloading thetransmitter. The sidelobe blocking oscillatorgenerates 0.6-µsec pulses, which are fed to thedecoders and to sidelobe detector CR301 andCR302. An additive memory network in thedetector combines pulses P1 and P2 to form asingle pulse with sufficient amplitude to trigger

sidelobe multivibrator V302. The output ofV302 is the sidelobe-suppression gate pulsecoupled through one-half of OR gate CR303and CR304 to the input of V301. Main gateinput is fed from the suppressor cathode- fol-lower section of V304 to the front panelSUPPR jack (J106) and to the other halfof V304 where the main gate suppression pulseis inverted and fed through the other half ofOR gate CR303 and CR304 to V301. Thesidelobe-suppression gate from V302 is fed tosidelobe AOC rectifier CR308. The main gatesuppression pulse output of V304 is fed tomain gate AOC rectifier CR305. The outputof the sidelobe and main gate AOC rectifiersare fed to OR gate CR307 and CR310. Thedc OR gate output is used to control IF ampli-fiers V202, V203, and V204 sensitivity and toprevent overload of the transponder set trans-mitter.

b. Spike Suppressor (fig. 19.1). The positivevideo input pulses at pin No. 7 of card con-

5

C7-TM 11-5895-217-35

nector P301 are coupled through capacitorC308 and developed across resistor R321. Thesepulses are applied simultaneously to the sup-pressor grid of spike suppressor V303 and 0.3-µsec delay line DL301. The output of DL301,occurring 0.3 µsec after the input, is appliedacross resistor R322 to the control grid ofV303. Both grids are biased to cutoff by volt-age from the -150-volt dc distribution bus(para 42) input at pin No. 10 of card connec-tor P301. Tube V303 is able to conduct onlywhen the suppressor grid and control grid areboth driven positive by pulses simultaneously.Noise pulses of 0.3 µsec or less at the suppres-sor grid will not be in coincidence with thesame pulses at the control grid due to DL301.Without coincidence, V303 will not conductthe 0.3-µsec noise pulses into the output. Platevoltage for V303 is supplied from the +125-volt dc distribution bus (para 41e ) through theprimary of transformer T302, isolation filterresistor R323, and capacitor C310. The sec-ondary of transformer T302 feeds 0.4 µsecpositive interrogation pulses through capacitorC309 to the input of sidelobe blocking oscilla-tor V301.

c. Sidelobe Blocking Oscillator (fig. 20.1).The input section of sidelobe blocking oscilla-tor V301 acts as a trigger amplifier, which hascontol grid pin 2 biased to cutoff by voltagedivider R301 and R302 from the -150-volt dcdistribution bus (para 42). Positive interroga-tion pulses fed through capacitor C309 fromV303 cause the input section of V301 to con-duct plate current, through winding 3-4 oftransformer T301, supplied from the +125-VOJ distribution bus (para 41e ). Pulse cur-rel. winding 3-4 of T301 induces a positivepulse in winding 1-2 of T301, which is appliedto control grid pin 7 of V301, The control gridpin of V301 is fixed biased through resistorR306 and winding 1-2 of T301 by a voltagedivider consisting of resistors R305 and R307.A positive pulse at grid pin 7 further increasesthe pulse current in winding 3-4 of T301 dueto the common plate connection of V301, whichin turn causes V301 to become saturated.Capacitor C301 eliminates degeneration causedby cathode resistors R303 and R304. During

the positive swing of V302, capacitor C302 ischarged at a rate determined by the settingof resistor R306. After the trigger pulsereaches maximum amplitude, the rate of platecurrent change begins to diminish, and thevoltage of T301 winding 1-2 reduces. Whenthe charge voltage of capacitor C302 equalsthe voltage across T301 winding 1-2, they can-cel due to polarity opposition. The static fixedbias then cuts off control pin 7 of V301 andthe magnetic field of transformer T301 beginsto collapse, reversing T301 winding 1-2 volt-age. This reversal drives control grid pin 7of V301 further into cutoff, sharpening thetrailing edge of the generated pulse. The posi-tive pulses taken from the junction of cathoderesistors R303 and R304 are adjusted to awidth of 0.6 µsec by resistor R306 and are fedto decoders V351, V352, and V353 throughpin 2 of card connector P301. A third winding(5-6) on transformer T301 is swamped by

resistor R339 to prevent ringing and this wind-ing supplies blocking oscillator pulses throughcapacitor C303 to the sidelobe detector circuit.Sidelobe-suppression gate pulses (e below)from V302 are fed to the trigger input ofV301 through diode CR303 to cut off V301immediately after the receipt of an SLS con-trol pulse (P2). The negative sidelobe-suppres-sion gate pulse cuts off V301 to prevent inter-rogation pulses P3 from reaching decodersV351, V352, and V353 and thus controlstransponder set replies in accordance withcontrol pulse P2. Negative main gate pulses(f below) from V304 are fed to the triggerinput of V301 through diode CR304 to cutoff V301 after one proper interrogation is re-ceived. Diodes CR303 and CR304 form an ORgate which permits either gate to cut off thetrigger section of blocking oscillator V301.

d. Sidelobe Detector (fig. 20.1). Sidelobe de-tector diode CR302, in conjunction with ca-pacitor C303 and resistor R309, forms amemory circuit for the sidelobe blocking os-cillator (V301) pulses triggered by interroga-tion pulse P1. Diode CR302 is forward biasedby voltage divider resistors R308 and R309and the +125-volt dc distribution bus (para41e). During the time that V301 is cutoff (no

6

C7-TM 11-5895-217-35

pulse output), capacitor C303 is discharged toground due to low resistance of CR302. WhenV301 is triggered by P1 only, the output nega-tive swing of T301 winding 5-6 cuts off CR302and the negative pulse portion of the outputis developed across R309. As the voltage acrosswinding 5-6 goes through the reference levelin the positive direction, CR302 again conductsand effectively grounds one side of capacitorC303. Capacitor C303 then charges to the posi-tive peak voltage across T301 winding 5-6developed by the positive pulse portion of V301output. As the positive pulse begins to gonegative toward the reference level, diodeCR302 again cuts off and capacitor C303 dis-charges developing the second negative pulseacross R309. The separation time between thefirst negative pulse and the second negativepulse (P1 memory pulse) is the sum of theblocking oscillator output pulse widths (nega-tive and positive swings), and the rc timeconstant of C303 and R309 determines aper-ture (memory pulse width), which results ina P1 memory pulse position of approximately2.0 µsec. Triggering of blocking oscillator V301by a P2 SLS pulse at 2.0 µsec results in anoverlap of the blocking oscillator negative out-put pulse and the P1 memory pulse; the P2memory pulse is of no importance to circuitoperation. The P2 pulse and the P1 memorypulse are additive and result in a single pulseapproximately double the amplitude of eitherof the two pulses developed by P1 alone.Diode CR301 is biased to cutoff by a voltagedeveloped across voltage divider resistorsR310, R311, R312, and R313 connected be-tween ground and a -150-volt dc distributionbus (para 42). The amount of negative biasis adjusted by control R311 to prevent CR301from conducting on a P1 pulse only. However,when a P2 pulse is added to the P1 memorypulse, the resultant amplitude is enough tocause CR301 to conduct the P2 pulse to R312and R313. Capacitor C304 couples the P2 pulseto the input of sidelobe multivibrator V302.

e. Sidelobe Multivibrator (fig. 21.1). Gridpin 2 of tube V302 is biased positive by re-sistors R314 and R315 connected to the +125-volt dc distribution bus to cause plate current

saturation. Identical plate load resistors R317and R318 are used for both sections of tubeV302, and grid pin 7 is negative biased withvoltage divider resistors R319 and R320 con-nected from the -150-volt dc distribution busto plate pin 1. Capacitors C305 and C306 arefeedback coupling capacitors. When a negativesidelobe detector trigger pulse is coupledthrough capacitor C304 to grid pin 2, pin 1plate current is driven to cutoff; this actiondrives grid pin 7 positive. Grid pin 7 goingpositive, increases pin 8 plate current and thenegative plate voltage swing is coupled backthrough C305 to hold grid pin 2 at cutoff. Thesidelobe detector trigger pulse has collapsedby this time, pin 1 plate current is cut off, andpin 8 plate current has reached saturation.The multivibrator pulse width is determinedby the discharge rates of capacitors C305 andC306 and the setting of R315. Adjustment ismade for a pulse width of 35 µsec and thenegative sidelobe gate pulse is taken fromplate pin 8. Capacitor C307 is the couplingcapacitor for input through OR gate diodeCR303 to blank V301 for sidelobe suppression(d above). Diode CR314 clips any positivepeaks occurring on the gate pulse and aids indecreasing pulse delay time which shortensreinitiation time after sidelobe suppression.Diode CR314 has its cathode biased positiveby voltage supplied from the +125-volt dcdistribution bus through voltage divider re-sistors R342 and R343, and limits the positiveswing of plate pin 8. Diode CR315 has itsanode biased negative by voltage supplied fromthe -150-volt dc distribution bus throughvoltage divider resistors R340 and R341, andlimits the negative swing of grid pin 7 to de-crease reinitiation time after sidelobe suppres-sion. This action steepens the leading andtrailing edges of the sidelobe gate pulse ob-tained from multivibrator V302.

f. Inverter Amplifier and Suppressor Cath-ode Follower (fig. 22.1). Main gate blankingpulses are fed to pin 9 of card connector P301through capacitor C313 to control grid pin 2of suppressor cathode follower V304A. Thecontrol grid is fixed biased from the -150-voltdc distribution bus through voltage divider

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C7-TM 11-5895-217-35

resistors R329 and R330. Plate voltage is sup-plied direct to pin 1 of V304A from the +125-volt dc distribution bus. A positive main gatesuppression pulse is developed across V304Acathode resistor R331, and diode CR313 couplesonly the positive portion to card connectorP301 pin 13 which connects to the front panelSUPPR jack J106. The main gate suppressionpulse is developed across resistor R334 andcoupled through capacitor C315 and resistorR333 to control grid pin 7 of inverter ampli-fier V304B. Grid bias is supplied from the-150-volt dc distribution bus through voltagedivider resistors R335 and R336. Plate voltagefor V304B is supplied from the +125-volt dcdistribution bus through plate load resistorR332. The amplified negative output pulsesfrom V304B are fed through coupling capacitorC314 to blocking oscillator V301 and to maingate A.O.C. rectifier diode CR305; diode CR312removes any positive peaks from the negativemain gate suppression pulse.

Page 34. After figure 22, add figure 22.1.

g. A.O.C.(fig. 22.1).pulses from

Rectifiers, Switches, and OR GatesNegative main gate suppression

V304B are rectified by CR305 andare fed to a filter network consisting of resis-tors R325 and R326 and capacitor C311. Thedischarge rate of capacitor C311 is governedby the adjustment of R326 and determines thecounting rate of gate pulse input. If the maingate pulse recurrence response (prr) exceedsthe preset value, the voltage developed acrossR326 and C311 will close Zener diode switchCR306 and pass the resultant dc bias voltagethrough OR gate diode CR307 to card connec-tor P301 pin 12 to IF amplifiers V202, V203,and V204. Sidelobe A.O.C. rectifier CR308,switching diode CR309, and OR gate diodeCR310 operate similarly with resistor R328and capacitor C312 determining the sidelobe-suppression gate A.O.C. count or thresholdfor sensitivity reduction of IF amplifiers V202,V203 and V204.

8

Figure 22.1. Inverter amplifier, suppressor cathode follower, and A.O.C. (SLS), partial schematic diagram.

C7-TM 11-5895-217-35

Page 49, figure 37 (page 3 of C 5). Add thefollowing note:

3. FOR THE RT-494B/APX-44, RE-SISTOR R454 HAS BEEN CHANGEDFROM 33,000 OHMS TO 24,000OHMS, RESISTOR R455 HAS BEENCHANGED FROM 100,000 OHMS TO22,000 OHMS, RESISTOR R456 HASBEEN CHANGED FROM 1.5 MEG-OHM TO 330,000 OHMS, AND CA-PACITORS C451, C454, AND C455HAVE BEEN CHANGED FROM0.01 µF TO 0.0047 µF.

Page 60, paragraph 41 (para 41 of O 5),heading. Delete and substitute:

41. B+ Distribution (RT-494/APX WithoutSLS, fig. 49; RT-494B/APX-44 WithoutSLS, fig. 49.1; RT-494/APX-44 WithSLS, fig. 49.2; RT-494B/APX44 WithSLS, fig. 49.3)

Page 61, paragraph 42, heading. Delete“(fig. 50)” and substitute:

(For Equipments Without SLS, figure 50;For Equipments With SLS, figure 50.1).

Page 73, paragraph 53. Make the followingchanges:

Line 10 (page 6 of C 5). After “(fig. 8)”,add: (SLS, fig. 8.2).Line 12. After “Figure 54” add: (SLS,fig. 54.1) .Paragraph 54b (3) (page 6 of C 5). After“(figs. 54 and 55)," add: (SLS, 54.1).

Page 74. After figure 54, add figure 54.1.

9

Figure 54.1.

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Page 82, paragraph 58c. Add the followingto the chart:

SchematicTest point and waveform

locationSubassembly

diagramfig. No. fig. No.

VIDEO AMPLIFIER/SLS card 113.13 124.1

Chart. Add after step 15:

Step

16

17

Oscilloscope

Green lead(pin 5) ofV303(fig. 76.1) .

Green lead(pin 5) ofV303(fig. 76.1).

Waveformreference

A, figure124.1(xmtroff).

C, figure124.1(xmtroff).

Normalindication

Positive interrogationpulses for eachmode with correctwaveshape and am-plitude at V303 suppressor and controlgrid.

Upper trace showspulses P1 and P2and no P3. Lowertrace shows pulsesP1/P2 with P3 insidelobe gate.

Page 94, figure 71 (page 7 of C 5), notes.Make the following changes:

Note 4. Add the following:FOR THE RT-494/APX-44 ONLY,RESISTANCE IS 450 K WITHMODE 2 CONTROL OFF AND 0

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Page 90, paragraph 59b (page 7 of C 5).Make the following changes:

Add after heading:

Note. Use steps 16 and 17 instead of steps 4 and 5when troubleshooting equipments with SLS capability.

Abnormalindication

No pulses, either gridV303.

No pulses at controlgrid of V303.

All three pulses onupper trace; nosidelobe gate onlower trace.

No pulses on eithertrace.

Pulse P1 and P3normal on uppertrace: no mail gateon lower trace.

Corrective measures

Check continuity between pin 7of J391 (fig. 106) and pin 3 ofP201 (fig. 105); repair wiring ifopen.

Replace or troubleshoot (para64.1) and repair video amplifier/SLS card as required.

Replace or troubleshoot (para64.1) and repair video amplifier/SLS card as required.

Replace or troubleshoot (para64.1) and repair video amplifier/SLS card as required.

Replace or troubleshoot (para64.1) and repair video amplifier/SLS card as required.

Replace or troubleshoot (para64.1) and repair video amplifier/SLS card as required.

Proceed to steps 6, 7, and 8, tocheck main gate multivibratorand amplifier.

Check for continuity between pin9 of J301 and pin 12 of J451(fig. 106). Repair wiring ifopen.

OHM WITH MODE 2 CONTROL ON.Note 5. Add the following:

FOR THE RT-494B/APX-44 ONLY,RESISTANCE IS 330 K WITHMODE 2 CONTROL OFF AND 22K WITH MODE 2 CONTROL ON.

11

Figure 75.1.

Page 99.

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Page 100. Add after paragraph 64:64.1. Video AmpIifier/SLS Card

Troubleshootinga. General. The chart (c below) lists trouble

and corrective maintenance procedures for thevideo amplifier/SLS card. All measurementsare made with receiver-transmitter completelyassembled unless otherwise specified. Use thebench test setup shown in figure 113.11. Referto the partial schematic diagrams (fig. 19.1through 22.1), complete schematic diagram(fig. 124.1), and parts location printed wiring

c. Video Amplifier/SLS Troubleshooting Chart.Item

1

2

3

4

5

6

7

8

9

Indication

No output to decoder card ----

No wave forms present at eithertest point A.

No SLS P2 pulse present ateither test point A.

No channel 2 waveform presentat test point A.

No waveforms present at testpoint B.

No waveforms present at testpoint C.

No waveform present at testpoint D with normal P1/P2pulses at test point C.

No waveforms present at testpoint E.

No SLS gate wave form presentat test point B with normalwaveform at test point E.

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diagram (fig. 76.1) for circuit connections.After trouble has been isolated, replace the de-fective part by following the procedures inparagraph 76.

b. Video Amplifier/SLS Voltage and Resis-tance Measurements. Tube voltage and resis-tance measurements shown in figure 75.1 aretaken with no signal input to the transponderset. Card receptacle voltage and resistancemeasurements (fig. 71) are also useful forisolating troubles.

Probable trouble

Open filament circuit- - - - -- - - -Defective stage in video ampli-

fier/SLS card.

No video input fromsor subchassis.

IF suppres

Suppressor circuit in IF sup.pressor subchassis defective.

Defective delay line DL301 ____

Defective spike suppressor stage

Defective sidelobe blocking oscil-lator stage.

Defective sidelobe detector cir-cuit.

Defective sidelobe multivibratorstage.

SLS OR gate inoperative ------

Procedure

Check filament circuit continuity.Check waveforms A, B, and C

(fig. 124.1) at test points (fig.76.1). Refer to items 2 through6 below.

Troubleshoot IF suppressor sub-chassis. (para 63).

Check wiring that connects pin 3of P201 to pin 7 of J301 (fig.122).

Troubleshoot suppressor circuit inIF suppressor subchassis (para63) for 10 dbm threshold at 2.0µsec from P1.

Replace DL301 (fig. 76.1).

Remove and check V303 (fig. 54.1and 76.1); replace if defective.

Make voltage and resistance checkof V303 stage (fig. 75.1).

Remove and check V301 (fig. 54.1and 76.1); replace if defective.

Make voltage and resistance checkof V301 stage (fig. 75.1).

Check diodes CR301 and CR303(fig. 76.1). Check adjustment ofR311 (para 90.3).

Remove and check V302 (fig. 54.1and 76.1); replace if defective.

Make voltage and resistance checkof V302 stage (fig. 75.1).

Check diodes CR303 and CR311(fig. 76.1).

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c. Video Amplifier/SLS Troubleshooting Chart. - (Continued)

Item

10

11

12

13

Indication

No waveform present at testpoint F.

No main gate waveform presentat test point B with normal

Probable trouble Procedure

No main gate input to video “Check for main gate output atamplifier/SLS from V454 in mode reply selector card (paramode reply selector card. 68).

Check wiring that connects pin 9of J301 to pin 12 of P451 (fig.122).

Defective inverter amplifier and Remove and check V304 (fig.suppressor cathode follower 54.1 and 76.1); replace if de-stage. fective.

Make voltage and resistance checkof V304 stage (fig.

Main gate OR gate inoperative Check diodes CR304(fig. 76.1) .

waveform at test point F.SLS A.O.C. inoperative with SLS A.O.C. rectifier, switch or

normal waveforms at test gate defective.point B.

with normal spurious reply Main gate A.O.C. rectifier,pulse blanking normal; wave- switch, or gate defective.forms at test point B normal.

Check diodes CR308,CR310.

Check adjustment of90.5).

Check diodes CR305,CR307.

Check adjustment of90.6).

75.1).and CR312

CR309, and

R328 (pars

CR306, and

R326 (para

14

Figure 107.2

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Page 108, figure 83, notes (page 7 of C 5). Page 129 (page 15 of C 5). After figureAdd the following to note 5: 107.1, add figure 107.2:

FOR THE RT-494B/APX-44 ONLY, Page 139. Make the following changes:PIN 5 RESISTANCE IS 20 K. Add section II.I and figures

113.13 after section II.

Section II.I. VIDEO AMPLIFIER/SLS CARD ADJUSTMENTS

113.7 through

88.1. Test Facilities Required alents will be required for performing theThe following equipments or suitable equiv- VIDEO AMPLIFIER/SLS (SLS) card ad-

justments.

a. Test Equipment.

Equipment Federal stock

No.1

Test Set, Radar AN/UPM-135-- - - - - - - - - - - - - - - - -Multimeter ME-26B/U . . . . . . . . . 6625-646-9406Oscilloscope AN/USM-140 ______ -----------------------Test Set, Transponder AN/APM- - - - - - - - - - - - - - - - -

123(V)1.

b. Additional Equipment.(1)

(2)

(3)

(4)

(5)

16

A 27.5-volt (± 0.25), dc power sup-ply with 7.5-ampere output (PowerSupply PP-1104A/G, or equivalent)is required to provide an input voltagefor the transponder set.A wire harness is required to connectthe receiver-transmitter to Control,Transponder Set C-2614/APX-44and to the de power supply. The wireharness may be fabricated by usingthe connectors and electrical wireshown in figure 3.A test panel with provision for ad-justment of the VIDEO AMPLI-FIER/SLS card is required to replacethe receiver-transmitter right-handside panel to enable behind-the-paneladjustments to the receiver-transmit-ter with a panel in place. The testpanel is fabricated in accordance withthe instructions in paragraph 88.2.A jeweler’s screwdriver set (FSN5120-288-8739) is required for ad-justments of R328 (SIDELOBEA.O.C.) and R326 (MAIN GATEA.O.C.).A 25-watt, 50-db attenuator (A8401S,

Qty reqd

1111

TM 11-6626-200-12TM 11-6626-535-15TM 11-6626-667-12

Commonname

Test setVtvmOscilloscopeTransponder

Engleman Microwave Company orequivalent).

88.2. Test Panel Fabrication With ProvisionFor SLS Adjustment

Fabricate the test panel in accordance withthe dimensions shown on figures 113.7, 113.8,and 113.9, the test panel markings, A.O.C.TEST VOLTS pin jack detail, and DETWAVEFORM pin jack detail shown on figure113.10, and the procedures given in a throughp below.

a. Use a sheet of soft aluminum (type 6061-T6, or equivalent), 0.050 inch thick, 7 7/8 incheswide, and 19 9/16 inches long to fabricate thetest panel.

Note. As an alternate, a discarded receiver-trans-mitter right-hand side panel may be used for the testpanel or a test panel previously fabricated from in-structions in paragraph 100 (page 2 of C 3) andmodified in accordance with the instructions in c, e, h,j, m, n, and p below.

b. Bend the sheet of aluminum 3/8 inch fromthe bottom edge along the 19 9/16 -inch dimen-sion.

Note. The bend provides a ledge which inserts intofasteners on the inside bottom of the receiver-trans-mitter.

C7-TM 11-5895-217-35

c. Drill out all the holes and cut out the j. Install the two door runners with rivetsrectangular hole in accordance with the dimen- and install the sliding door in accordance withsions shown on figure 113.7. instructions on figure 113.9.

d. Install a turnlock stud fastener (Camloc k. Cut a piece of clear plastic tubing 7/16 -

No. 555-6) with a stud retaining washer inch inside diameter and 3 5/8 inches long (fig.(Camloc No. 553-1) into each of the seven 137 (page 6 of C 3)).3/16-inch mounting holes.

e. Set and secure the drilled-out test panelin place on the receiver-transmitter. Check thealignment of the test panel holes with the re-ceiver-transmitter controls and test points(SLS card installed). The location of the con-trols and test points for each individual re-ceiver-transmitter may be slightly different.If necessary, mark the area around the holesthat require additional cutting away, removethe test panel, and use a round file to cut awaythe marked area.

Note. The plastic tubing is used as a screwdriverguide when variable resistor R154 requires adjustment.The plastic tubing is inserted through the BLOCKOSC hole and fits snugly over the locknut of variableresistor R154. When not in use, the plastic tubingmounts on a metal strip directly below the BLOCKOSC hole.

l. Fabricate a rigid metal strip 1/16 inchthick, 7/16 inch wide, and 2 7/8 inches long.Mount the metal strip with a 1/4-inch spacer,bolt, and nut to the test panel directly under

f. Place a plastic tubing insert that has a lip the BLOCK OSC hole. Insert the 1/4-inchspacer between the metal strip and test panelon one end (fig. 137 (page 6 of C 3)) into each to enable the plastic tubing (k above) to slideof the four 13/32-inch holes. When installed,

the plastic insert should fit snugly into the over the metal strip.

hole, and the lip should be exposed on the out- m. Install an insulated pin jack with groundside of the test panel. Secure the plastic insert lug in place into the 1/4-inch A.O.C. TESTwith glue. VOLTS hole on the test panel (fig. 113.10).

Note. The plastic inserts prevent the oscilloscope testprobe from shorting to the test panel.

g. Fabricate eight 15/16-inch diameter disksand two 1 1/4-inch disks from a sheet of alum-inum, 0.050 inch thick.

h. Fabricate two door runners and one slid-ing door from instructions on figure 113.8.

i. Install the disks with rivets so that thedisks are capable of swinging away from theholes they cover, in at least one direction, with-out interfering with the adjacent disk. Use a1/64-inch spacer between the test panel andeach disk that covers a. 13/32-inch hole. (Thedisks must be raised from the test panel toclear the lip of the plastic insert.) One each1 1/4-inch disk spans the COINCIDENCE andRING OSC hole.

Note. Remove paint from test panel area that makescontact with the ground lug.

n. Install an insulated pin jack into the 1/4-inch DET WAVEFORM hole on the test panel.

o. Solder one end of a 9-inch long, flexible,insulated wire (#20) to the lug on the A.O.C.TEST VOLTS pin jack. Solder the other end ofthe wire to a connector that mates with theA.O.C. test pin on the IF amplifier subchassis.

p. Solder one end of a 9-inch long, flexible,insulated wire (#20) to the lug on the DETWAVEFORM pin jack. Solder the other endof the wire to a connector that mates with theDET test pin on the IF amplifier subchassis.

17

Figure 113.7.

C7-TM

11-5895-217-35

18

Figure 113.8.

C7-TM

11-5895-217-3519

Figure 113.9.

C7-TM

11-5895-217-35

20

C7-TM 11-5895-217-35

Figure 113.10. Receiver-transmitter with SLS test panel in place.

21

C7-TM 11-5895-217-35

88.3. General Adjustment Requirementsa. Each procedure must be performed in the

sequence outlined in (1) through (11) below.Do not vary the sequence because the validityof each adjustment or test procedure dependsupon the completion of an immediate pre-ceding procedure.

(1)(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

( l o )

(11 )b. Do

Preliminary procedures (para 88.4).Preliminary panel control settings(para 88.5).Adjustment of signal generator fre-quency (para 88.6).High receiver sensitivity and maingate A.O.C. adjustment (para 88.7).Sidelobe blocking oscillator adjust-ment (para 88.8).Preliminary sidelobe detector adjust-ment (para 88.9).Sidelobe multivibrator adjustment(para 88.10).Sidelobe-suppression minimum rangeadjustment (para 88.11).Sidelobe-suppression maximum rangetest (para 88.12).Preliminary sidelobe A.O.C. controladjustment test (para 88.13).Operational check (para 88.14).not make any tests on the receiver-

transmitter unless the test panel is in placebecause the test results will not be valid. Testpanel openings must be closed with theircovers when an adjustment is not being madethrough the opening. Do not remove the left-hand panel.

c. Minimum warmup time for the receiver-transmitter must be at least 45 minutes. Thiswarmup time must be observed so that theinternal temperature of the receiver-transmit-ter can stabilize to the same temperature con-dition as that of an equipment in normaloperating use. A stabilized temperature condi-tion can only be achieved with the test panelin place and all test panel openings and slidingdoor closed. If the receiver-transmitter tem-perature is not stabilized, the different tem-perature levels will cause a changing A.O.C.voltage that will invalidate the A.O.C. and re-ceiver sensitivity adjustments (para 88.7) and

cause the receiver-transmitter to perform er-ratically and poorly in tactical operation.

88.4. Preliminary Proceduresa. Construct a wire harness (fig. 3) for use

in interconnecting the receiver-transmitter toControl, Transponder Set C-2714/APX-44,and to the dc power supply.

b. Construct a test panel with provision foradjustment of the SLS card (para 88.2) foruse in replacing the right-hand panel on thereceiver-transmitter to enable behind-the-paneladjustments to the receiver--transmitter witha panel in place.

c. Remove the receiver-transmitter right-hand panel. Connect the alligator clip attachedto the flexible lead from the A.O.C. TESTVOLTS pin on the test panel to the A.O.C. testpin on the receiver-transmitter IF amplifiersubchassis. Connect the alligator clip attachedto the flexible lead from the DET WAVEFORMpin on the test panel, to the DET pin on thereceiver-transmitter IF amplifier subchassis.Position and secure the test panel in place onthe receiver-transmitter.

Note. Do not make any tests on the receiver-trans-mitter without the test panel in place.

d. Connect the equipment as shown in figure113.11.

e. Ground the case of Simulator, CoderSM-500/UPM-135, receiver-transmitter, andOscilloscope AN/USM-81 (oscilloscope) witha copper wire (#22 AWG). Make sure wiremakes contact with bare metal on each unit.

88.5. Preliminary Panel Control SettingsWith the equipment connected as shown in

figure 113.11, make the preliminary panel con-trol settings outlined in a through n below.Perform each control setting in the indicatedsequence.

a. DC Power Supply. Adjust output voltageof dc power supply to 27.5 volts.

b. Control Unit.(1) Set master control to STBY.

22

C7-TM 11-5895-217-35

(2) Set function contralto MOD.(3) Set MODE 2 ON-OFF switch to ON.(4) Set MODE 3 ON-OFF switch to ON.(5) Set MODE 1 code control to 00.(6) Set MODE 3 code control to 00.(7) Set AUDIO ON-OFF switch to OFF.(8) Set I/P switch to OFF.

c. Receiver-Transmitter. Set all mode 2 tog-gle switches to OFF.

d. All Equipment. Energize equipment. Al-low 30 minutes for all equipment to warm up.

e. Signal Generator (Part of SM-500/UPM-Set signal generator to 1,030 mc as follows:

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

Set CAL-CONTROL unit METERSELECT switch to CAL.Adjust CAL-CONTROL unit CALADJ control for a full-scale meter in-dication.Set CAL-CONTROL unit METERSELECT switch to WM.Turn CAL-CONTROL unit WMSENS control fully cw.Set WAVEMETER INPUT switch toSIG GEN.Set WAVEMETER FREQUENCYcontrol to a dial setting equivalent to1,030 mc in accordance with ap-propriate WAVEMETER CALIBRA-TION CURVE in Book of CalibrationCharts provided with AN/UPM-135.Vary SG FREQUENCY control fora dip on CAL-CONTROL unit meter.Turn CAL-CONTROL unit WMSENS control ccw and, at same time,vary SG FREQUENCY control untildip on meter occurs within range ofmeter scale.Set SG FREQUENCY control for amaximum dip on CAL-CONTROLunit meter.This completes the preliminary fre-quency adjustment.

f. Test Set, Radar AN/UPM-135.(1) Terminate LP IN Jack on SM-500/

UPM-135 with a 50-ohm only termi-nation plug.

(2)

(3)

(4)

Note. Some AN/UPM-135 terminationplugs are 50 ohms and others are 75 ohms.Check the resistance of the termination plugwith an ohmmeter to make sure that the re-sistance is 50 ohms.Set SYNC SELECT control to INTon XTAL MARK & SYNC unit.Set PRF control to approximately 6on XTAL MARK & SYNC unit.Make following control setting onINTERROGATION CODER unit:

(a)(b)(c)(d)

(e)(f)(g)(h)(i)

MODE SELECT switch to 1.SUB-PULSE counter control to 0.Function switch to MOD-INT.CODE WIDTH control approxi-mately two-thirds cw.VIDEO select switch to CODE.ISLS select switch to OUT.Subpulse select switch to OUT.ISLS level control fully ccw.ISLS WIDTH control approxi-mately two-thirds cw.

(5)

(6)

(7)

(8)

Set SM-500/UPM-135 ATTENUA-TION control fully ccw (minimumattenuation).Set CAL-CONTROL unit TRIGGERswitch to INT.Set CAL-CONTROL unit METERSELECT switch to 5,000 and VIDEOOUT control to SIG MON.Set DISPLAY unit VOLTS/IN switchto 5 and 75 ohms IN-OUT switch toOUT.

g. Oscilloscope AN/USM-81.(1) Make following control settings on

preamplifier:(a) MODE switch to A ONLY.(b) DC-AC slide switch to DC (on

CHANNEL A).(c) Black VOLTS/CM switch to .5 (on

CHANNEL A).(2) Make following MAIN SWEEP con-

trol settings:(a)(b)(c)

(d)

Black MULTIPLIER switch to 1.Black TIME/CM switch to 1.Red 5X MAGNIFIER switch toOFF.Black TRIGGER SLOPE switch toany position.

23

C 7-TM 11-5895-217-35

(e) Red TRIGGERING MODE switchto AC FAST.

(f) Red STABILITY control fully cw.(g) Black TRIGGERING LEVEL con-

trol fully cw.(3) Make following DELAY SWEEP

control setting:(a)

(b)(c)

(d)

(e)

Black TIME/CM OR DELAYswitch to 10 MICRO SEC.Red LENGTH control fully CW.DELAY-TIME MULTIPLIER con-trol to read 4 in window.Black TRIGGERING LEVEL con-trol fully cw.Red STABILITY control fully cw.

(4) Make following HORIZONTAL DIS-PLAY control settings:

(a) Mode selector switch to DELAY-ING SWEEP.

(b) SLOPE toggle switch to +.(c) ATTEN toggle switch to X 1.

h. Connect CAL-CONTROL unit VIDEOOUT jack to CHANNEL A input jack onoscilloscope; use type CG-530F/U coaxialcable.

i. Connect XTAL MARK & SYNC unit OTRIGGERS jack to TRIGGER OR EXT.SWEEP IN jack on oscilloscope; use type CG-530F/U coaxial cable.

j. On oscilloscope, slowly rotate red DE-LAYING SWEEP STABILITY control ccwuntil proper pulse stabilization is obtained.

k. Adjust oscilloscope INTENSITY controlto discern brightened portion of horizontaltrace.

l. Adjust oscilloscope DELAY-TIME MUL-TIPLIER control to position brightened por-tion of horizontal trace over dual pulse mode1 interrogation.

m. Set oscilloscope HORIZONTAL DIS-PLAY mode selector switch to MAIN SWEEPDELAY.

n. Adjust controls as necessary to obtainan optimum display.

88.6. Adjustment of Signal GeneratorFrequency

Note. The calibration charts supplied with theAN/UPM-135 have been prepared to enable the signal

24

generator unit to be aligned accurately to within ±0.7mc. The crystal-controlled signal of the ISLS pulsegenerator (part of INTERROGATION CODER unit)is accurate to within ±0.2 mc of 1,030 mc. It is, there-fore, possible to further align the signal generatorfrequency output by zero-beating it against the fixedISLS signal, thereby obtaining a three pulse frequencyaccuracy of 1,030 ±0.2 mc. Proceed as follows:

a. Set ISLS select switch to 2 µsec, on IN-TERROGATION CODER unit, function switchto INT, and MODE SELECT switch to either1, 2, or 3A.

b. Turn XTAL MARK & SYNC unit PRFcontrol fully clockwise.

c. Adjust INTERROGATION CODER unitCODE WIDTH control for a P1, P3 pulsewidth of 0.8 µsec at half-amplitude points asviewed on oscilloscope.

d. Set INTERROGATION CODER unitISLS level control to 0 and adjust ISLSWIDTH control and screwdriver adjust CALcontrol so that middle ISLS pulse is equal inwidth and amplitude to the two interrogationpulses.

e. Set INTERROGATION CODER ISLSPULSE switch to CHECK.

f. Set the oscilloscope MAIN SWEEP:TIME/CM control to 0.1 µsec and MULT con-trol to 2 for a view of first pulse (P1) approxi-mately 4 centimeters wide.

g. Place oscilloscope hood over screen andslowly rotate SG FREQUENCY crank on SM-500/UPM-135 signal generator unit to eitherside of position previously set in preliminarysignal generator frequency adjustment (para88.5), and notice a beat indication on top ofdisplayed pulse. Observe that fill-in traceschange from vertical to horizontal and backto vertical. Set SG FREQUENCY crank forbest horizontal fill-in. This fill-in indicates azero beat (same frequency) between crystal-controlled P2 signal generated in INTERRO-GATION CODER unit and variable P1, P3signals generated in SM-500 135 signal gen-erator unit.

Note. The adjustment performed in g above is criti-cal; therefore, it requires absolute certainty beforecontinuing on.

h. Return PRF control on XTAL MARK& SYNC unit to approximately 6.

C 7-TM 11-5895-217-35

i. Set CAL-CONTROL unit METER SE-LECT switch to 500, and adjust XTAL MARK& SYNC unit PRF control for a reading of500 on CAL-CONTROL unit meter.

j. Disconnect video cable from VIDEO OUTjack on CAL-CONTROL unit and connectjumper cable CG-530/U (10 inches) betweenVIDEO OUT jack on CAL- CONTROL unitand VIDEO jack on DISPLAY unit. OnMAIN SWEEP, set TIME/CM control to 1and MULTIMETER switch to 1.

k. This completes the final signal generatorfrequency adjustment.

88.7. High Receiver Sensitivity and MainGate A.O.C. Adjustment

Notes:

1. Warm up the receiver-transmitter for at least30 minutes, so that the internal temperature ofthe receiver-transmitter can stabilize to thesame temperature condition as that of anequipment in normal operating use. A stabilizedtemperature condition can only be achieved withthe test panel in place and all test panel open-ings and sliding door closed. If the receiver-transmitter temperature is not stabilized, thedifferent temperature levels will cause achanging A.O.C. voltage that will invalidatethe A.O.C. and receiver sensitivity adjustmentsand cause the receiver-transmitter to performerratically and poorly in tactical operation.

2. Do not make any tests on the receiver-trans-mitter unless the test panel is in place, becausethe test results will not be valid. Test panelopenings must be closed with their covers whenan adjustment is not being made through theopening. Do not remove the left-hand panel.

a. With equipment connected as before, con-nect oscilloscope probe between oscilloscopeCHALLEL B connector and DET WAVE-FORM test jack on test panel.

b. Make following control settings on oscil-loscope:

(1)(2)

(3)

(4)

MODE switch to B ONLY.Black VOLTS/CM switch to .1(CHANNEL B).Red VARIABLE control cw to CALI-BRATED (CHANNEL B).DC-AC slide switch to DC (CHAN-NEL B).

(5) Red POLARITY switch to NORMAL(CHANNEL B).

c. Set INTERROGATION CODER ISLSselect switch to OUT.

d. Set WAVEMETER INPUT switch toOFF on panel of AN/UPM-135.

e. Set INTERROGATION CODER MODESELECT switch to 1.

f. Set signal generator unit ATTENUA-TION control fully counterclockwise. Set C-2714/APX-44 control unit master control toNORMAL.

Note. Receiver-transmitter should now be firing areply to each interrogation from the signal generatorunit.

g. Set CAL-CONTROL unit TRIGGERswitch to DEMOD and observe that the samereading is obtained on the CAL-CONTROLmeter as in paragraph 88.6.

h. Set XTAL MARK & SYNC DELAY andTRIGGER DELAY controls to 0; set RANGEcontrol on SWEEP & INTEN MARK unit to20-200 and turn SWEEP SPEED control toposition display.

i. Adjust DISPLAY unit HOR control forproper presentation of a two-pulse mode 1reply.

Notes:1.

2.

3.

If indications specified in g and i above arenot stable (meter flickers or pulses arc-over)or not displayed at all, check to see that equip-ment is properly connected and preliminarypanel control settings have been properly madeas outlined in paragraph 88.5.If connections and control settings did not re-quire correction and a stable display resulted,proceed to j below.If connections and control settings did requirecorrection, or if unstable condition still existsafter correction, SIDELOBE DETECTOR con-tol R311 may be excessively maladjusted. Turnadjustment screw of R311 (fig. 113.13) clock-wise until indications specified in g and i aboveare fully displayed and then continue turningadjustment screw clockwise for 5 revolutions.(Final adjustment of SIDELOBE DETECTORcontrol R311 will be performed later duringsidelobe-suppression minimum range adjust-ment.)

j. Set oscilloscope MAINCM knob to 1 MICROSEC.

SWEEP TIME/

25

C7-TM 11-5895-217-35

Note. The mode 1 interrogation pulses should bedisplayed.

k. Adjust signal generator unit ATTENUA-TION control clockwise until CAL-CONTROLunit meter oscillates at 250 position (50 per-cent triggering point). At same time, arc-overshould occur across base-line of transmittedpulses displayed on DISPLAY unit scope. Notesetting of ATTENUATION control.

l. Turn ATTENUATION control ccw 30 dbfrom setting noted in k above.

Note. Peak amplitude of interrogation pulses dis-played on oscilloscope should be 2.5 volts ±0.5. AdjustCHANNEL B VOLTS/CM black knob, as required, foran adequate display of pulses.

m. Set vtvm selector control to measure anegative voltage. Momentarily short vtvmcommon lead to DC lead and adjust ZEROADJ control for an indication of 0 volt.

n. Connect vtvm DC lead to A.O.C. TESTpin jack on test panel. Connect vtvm commonlead to ground lug on test panel.

o. Turn signal generator unit ATTENUA-TION control cw until arc-over occurs acrossbase of transmitted reply pulses as indicatedon the DISPLAY unit scope. Indication onvtvm should decrease at same time. Turn AT-TENUATION control ccw until arc-overacross the transmitted reply pulses fully disap-pears.p. Adjust MAIN GATE A.O.C. control R326

(fig. 113.13) through test panel opening foran indication of approximately 0.6 volt as ob-served on vtvm.

Note. Set vtvm RANGE control to 1V to obtain amore accurate indication.

q. Slowly adjust signal generator unit AT-TENUATION control clockwise until CAL-CONTROL unit meter oscillates at 250 position(50 percent triggering point).

r. Note ATTENTUATION control settingand add this figure to the fixed attenuationspecified on DEMODULATOR ATTENUA-TION CONSTANTS chart for SG IN to HPIN under 1030 MC column in Book of Calibra-tion Charts provided with the AN/UPM-135.Cable loss must be added to this vale. The CG-

26

409E/U (5 feet 2 1/8 inches) cable has a lossof approximately 1.25 db. The fixed attenua-tion value will vary for each individual N/UPM-135. The total attenuation to achievethe 50-percent triggering point should be be-tween 80 and 86 db (that is, input voltagebetween -80 and -86 db per volt).

Note. If total attenuation is not at least 80 db,adjustment of HI SENS control R225 may be neces-sary and then, in turn, alignment of IF amplifier mayalso be necessary. (Refer to TM 11-5895-217-35 foradjustment and alignment procedures.)

s. Repeat procedures given in q and r abovewith MODE SELECT switch on INTERROGA-TION CODER unit set to 2 and then to 3/A.

t. Set INTERROGATION CODER unitMODE SELECT switch to 1.

u. Turn signal generator unit ATTENUA-TION control fully ccw (minimum attenuation,maximum signal).

v. Set CAL-CONTROL unit METER SE-LECT switch to 5000.

w. Set vtvm RANGE control to 10V.x. Observe reply pulses on DISPLAY unit

scope and slowly turn XTAL MARK & SYNCunit PRF control cw until arc-over first occursacross baseline of reply pulses. At this point,CAL-CONTROL unit meter should indicatenot more than 1,000. Slowly turn PRF con-trol further cw through its range. Arc-overacross pulses should increase in intensity andmeter indication should not be more than 1,000.If meter indicates more than 1,000, trouble-shoot main gate A.O.C. circuit.

y. Turn XTAL MARK & SYNC unit PRFcontrol ccw for an indication of 500 on CAL-CONTROL unit meter.

z. Set CAL-CONTROL unit METER SE-LECT switch to 500.

aa. Set vtvm RANGE control to 1V.ab. Set C-2714/APX-44 master control to

STBY.

88.8. Sidelobe Blocking OscillatorAdjustment

Notes:1. The high receiver sensitivity and main gate

A.O.C. adjustment (para 88.7) must be per-formed before proceeding with the followingprocedure.

C 7-TM 11-5895-217-35

2. Connections andperformed in themain gate A.O.C.

last setting of controls ashigh receiver sensitivity andadjustment remain the same

unless indicated otherwise.

a. Set ATTENUATION control fully coun-terclockwise on signal generator unit (maxi-mum attenuation).

b. Capacity couple alligator tip of probe togreen lead (pin 5) of V301 (fig. 113.13) bygrasping green lead with teeth of alligator tipthrough sliding door in test panel.

c. Adjust SIDELOBE BLOCKING OSCcontrol R306 so that width of first interroga-tion plus is 0.6 µsec at half-amplitude point.Notes:

1. Peak amplitude will depend upon amount ofcapacity coupling between probe and green lead(pin 5) of V301.

2. After adjustment, make sure that when R306adjustment screw is turned at least 2 revolu-tions cw from its adjusted position and thenat least 2 revolutions ccw from its adjustedposition, no abrupt change in pulse width willoccur (to insure stability in tactical operation).The point at which an abrupt change occursis the functional limit of R306.

d. Remove probe from green lead and closesliding door on test panel.

88.9.

Notes:1.

2.

Preliminary Sidelobe DetectorAdjustment

The sidelobe blocking oscillator adjustment(para 88.8) must be performed before proceed-ing with the following procedure.Connections and last setting of conrols as per-formed in the sidelobe blocking oscillator ad-justment remain the same unless indicatedotherwise.

a. Set up oscilloscope for CHANNEL Boperation and, using probe, monitor DETWAVEFORM test point on test panel.

b. Set INTERROGATION CODER unitISLS select switch to 2 µsec, and rotate ISLSlevel control clockwise to 0 to observe presenceof a P2 pulse.

c. Open sliding door on test panel, removeprobe from DET WAVEFORM test point andcapacity couple alligator tip of probe to redlead (pin 2) of V302 by grasping red leadwith teeth of alligator tip, to observe triggerpulse input to sidelobe multivibrator V302.

d. A negative trigger waveform should ap-pear on oscilloscope.

Note. Peak amplitude will depend upon amountof capacity coupling between probe and red lead (pin2) of V302.

e. Adjust INTERROGATION CODER unitISLS level control counterclockwise to -9DBmark and observe disappearance of triggerwaveform on oscilloscope.

f. If the desired conditions in d and e aboveare not present, SIDELOBE DETECTOR con-trol R311 may be maladjusted.

g. To correctly adjust R311, position IN-TERROGATION CODE ISLS level control to-9DB and adjust SIDELOBE DETECTORcontrol R311 until the negative-going pulse atpin 2 V302 just disappears.

h. Readjust INTERROGATION CODERISLS level control to 0 and observe presenceof negative-going pulse at pin 2 of V302.

Note. The procedures in g and h above may haveto be repeated several times until desired ISLS opera-tion is observed.

88.10. Sidelobe Multivibrator Adjustment

Notes :1. The preliminary sidelobe detector adjustment

(para 88.9) must be performed before proceed-ing with the following procedure.

2. Connections and last setting of controls as per-formed in preliminary sidelobe detector adjust-ment remain the same unless indicated other-wise.

a. Set ISLS level control to 0 on INTER-ROGATION CODER.

b. Capacity couple alligator tip of probe togray lead (pin 8) of V302 by grasping graylead with teeth of alligator tip, to observefiring of sidelobe multivibrator V302.

c. Set oscilloscope MAIN SWEEP MULTI-PLIER to 5 and TIME/CM to 1 µsec.

d. Adjust SIDELOBE MAIN GATEWIDTH control R315 to obtain a sidelobe gatepulse width from 30 to 35 µsec at half-ampli-tude point.

e. Remove alligator tip of probe from graylead (pin 8) of V302 and close sliding door ontest panel.

27

C 7-TM 11-5895-217-35

88.11. Sidelobe-Suppression MinimumRange Adjustment

Note. The sidelobe multivibrator adjustment (para88.10) must be performed before proceeding with thefollowing procedure.

a. With equipment connected as before, con-nect test probe between oscilloscope and DETWAVEFORM jack on test panel (to monitorthe spacing of the mode interrogations). SetMAIN SWEEP TIME/CM to 1.Notes:

1. The test probe must be used for connectionbetween the oscilloscope and the DET WAVE-FORM jack on the test panel. A direct cableconnection between the oscilloscope and the DE Tjack on the test panel will load down the circuitfeeding the DET jack and cause an undesirablechange in spacing between the interrogationpulses at the input of the video amplifier/SLScard.

2. The output from the receiver-transmitter RCVROUT jack must not be used for measurementof the mode interrogation pulse spacing. Useonly the DET WAVEFORM jack on the testpanel. The mode interrogation pulse spacingat the RCVR OUT jack is different from thatat the DET WAVEFORM jack and differentfrom that of the SM-500/UPM-135 signal gen-erator unit. Because of the different outputsat the RCVR OUT jack and the signal genera-tor unit, only the similar outputs of the DETWAVEFORM jack and signal generator unitcan be used for adjustment of the video am-plifier/SLS card.

b. Set INTERROGATION CODER unitISLS select switch to OUT (no P2 pulse out-put) .

c. Set control unit master control to NOR-MAL.

d. Set signal generator ATTENUATIONcontrol fully ccw (for minimum attenuationand maximum P1 and P3 pulse output).

e. With INTERROGATION CODER unitMODE SELECT switch alternately set to 1, 2,and 3/A, receiver-transmitter should fire fullyas indicated on the oscilloscope.

Note. Full firing is indicated by no random arc-over across the baseline of the transmitted replypulses from the receiver-transmitter and no downwardflicker (coincidental with the arc-over) on the CAL-CONTROL meter from its 500 prf position.

f. Set the INTERROGATION CODER unitMODE SELECT switch to 1.

28

g. Adjust oscilloscope controls, as required,for optimum presentation of mode 1 interroga-tion pulses.

h. Check to see that leading edge of firstmode 1 interrogation pulse is displaced 3.0 usedfrom leading edge of second mode 1 interroga-tion pulse at half-amplitude point.

i. Set INTERROGATION CODER unitISLS select switch to 2 µsec and adjust ISLSlevel control to 0.

j. Capacity couple alligator tip of probe togray lead (pin 8) of V302 (fig. 113.13) bygrasping gray lead with teeth of alligator tipthrough sliding door opening on test panel.

Notes:1.

2.

3.

Receiver-transmitter should not fire a reply atall, as indicated by disappearance of trans-mitted reply pulses (normally observed on DIS-PLAY unit scope when receiver-transmiter firesa reply).The CAL-CONTROL unit meter should indicate0 with no upward flicker (full suppression oftransmitted reply).The sidelobe suppression gate pulse, monitoredfrom gray lead (pin 8) of V302. should firefully with no arc-over.

k. Turn INTERROGATION CODER ISLSlevel control to -9DB and observe that thesidelobe suppression pulse ceases to fire onoscilloscope.

l. The CAL-CONTROL unit meter shouldindicate 500 with no downward flicker (fullfiring of transmitted reply).

m. Repeat the instructions in h through li..t””, with MODE SELECT switch set to 2and then to 3/A on INTERROGATIONCODER unit to determine that for a nominal2.0- ci: P2 pulse spacing (leading edge of P1p: and leading edge of P2 pulse at half-amplitude point) proper ISLS action occurs(full transmission when P2 is less than P1/P3by 9 db and full suppression, no transmission,when P2 equals P1/P3).

n. Return INTERROGATION CODER unitMODE SELECT switch to 1 and ISLS levelcontrol to 0.

o. Monitor DET WAVEFORM test point ontest panel with oscilloscope probe.

p. Set INTERROGATION CODER unit sub-pulse select switch to P2 and adjust SUB-

C 7-TM 11-5895-217-35

PULSE counter control to set spacing betweenleading edge of P1 pulse and leading edge ofP2 pulse to 1.85 µsec at half-amplitude point,and then to 2.15 µsec. At 1.85 µsec and 2.15µsec settings, with MODE SELECT switchalternately set to 1, 2, and 3/A, receiver-trans-mitter should not fire at all (transmitted replyfully suppressed), as indicated on DISPLAYunit scope.

Note. If performance standards given above aremet, SIDELOBE DETECTOR control R311 need notbe adjusted. If performance standards are not met,adjust SIDELOBE DETECTOR control R311 as re-quired.

q. On INTERROGATION CODER unit, setSUB-PULSE counter control to 0, subpulseselect switch to OUT, and ISLS select switch toOUT (no P2 pulse).

r. Check to make sure that receiver-trans-mitter does not fire on a single pulse interroga-tion by momentarily setting INTERROGA-TION CODER unit MODE SELECT switch toSGL. Reset MODE SELECT switch to 1.

s. If the transmitter fires on a single pulse,SIDELOBE DETECTOR control R311 must bereadjusted and the procedures in a through rabove must be repeated.

88.12. Sidelobe-Suppression MaximumRange Test

Notes:1. The sidelobe-suppression minimum range ad-

justment (para 88.11) must be performed be-fore proceeding with the following procedure.

2. Connections and last setting of controls as per-formed in the sidelobe-suppression minimumrange adjustment remain the same unless other-wise indicated.

a. Set control unit master control to NOR-MAL.

b. Turn signal generator unit ATTENUA-TION control cw until 50-percent triggeringis noted on CAL-CONTROL unit meter.

c. Turn signal generator unit ATTENUA-TION control 10 db ccw from 50-percent trig-gering point set in b above.

d. Adjust oscilloscope VOLTS/CM controlto adequately display P1 and P3 mode 1 inter-rogation pulses.

e. On INTERROGATION CODER unit, set

ISLS select switch to 2 µsec and ISLS levelcontrol to 0 (amplitude of P2 pulse is same asthat of P1 and P3 pulses).

f. Set INTERROGATION CODER unitMODE SELECT switch alternately to 1, 2,and 3/A. Receiver-transmitter should not firea reply at all, as indicated by disappearance oftransmitted reply pulses (normally observed onDISPLAY unit scope when receiver-trans-mitter fires a reply). The CAL-CONTROLunit meter should indicate 0 prf with no up-ward flicker.

g. Adjust ISLS level control ccw (decreaseP2 to -9DB); the transmitted reply pulsesshould appear and fire fully, without any arc-over (as observed on DISPLAY unit scope)and CAL-CONTROL unit meter indicates 500prf without downward flicker.

h. Set MODE SELECT alternately to 1, 2,and 3A on INTERROGATION CODER unit.Receiver-transmitter should fire fully in allmodes.

i. Adjust INTERROGATION CODER unitISLS level control clockwise to 0 (P2 equal toP1/P3).

j. On INTERROGATION CODER unit, setsubpulse select switch to P2 and adjust SUB-PULSE counter control to set spacing betweenleading edge of P1 pulse and leading edge ofP2 pulse to 1.85 µsec at half-amplitude point,and then to 2.15 µsec. At both these spacings,with MODE SELECT switch alternately set to1, 2, and 3/A, transmitted reply should remainfully suppressed as indicated on DISPLAYunit scope and 0 prf indication on CAL-CON-TROL unit meter.

k. Return ISLS select switch and subpulseselect switch to OUT, and SUB-PULSE countercontrol to 0.

88.13. Preliminary Sidelobe A.O.C. ControlAdjustment

The sidelobe-suppression maximum range test(para 88.12) must be performed before pro-ceeding with the following procedure. Connections and setting of controls as performed

in the preceding procedures remain the sameunless indicated.

29

C7-TM 11-5895-217-35

3. The sidelobe A.O.C. control adjustment approxi-mately determines the correct adjustment ofSIDELOBE A.O.C. control R328. Final ad-justment of R328 is a depot function: however,the adjustment of R328 in the procedure belowwill be sufficiently accurate.

a. Set INTERROGATION CODER unitMODE SELECT switch to 1.

b. Set master control switch on control unitto NORMAL.

c. Adjust oscilloscope controls to displaymode 1 P1 and P2 interrogation pulses fromDET WAVEFORM test jack on test panel.

d. Set subpulse select switch to P3 on theINTERROGATION CODER.

e. On INTERROGATION CODER unit, ad-just SUB-PULSE counter control ccw untilleading edge of P1 interrogation pulse isspaced exactly 2.0 µsec from leading edge ofsecond interrogation pulse, at their half-amplitude points, on oscilloscope.

Note. In e above, the second interrogation pulseis used as the P2 pulse, with a P3 pulse not present.

f. The vtvm indication should decrease to 0or slightly below 0 (as determined bytemporarily removing test lead probe fromA.O.C. TEST VOLTS jack on test panel, todetermine meter movement).

g. Connect RCVR OUT jack on receiver-transmitter to oscilloscope CHANNEL A jack,using CG-530F/U video cable.

h. Set CAL-CONTROL unit TRIGGERswitch to INT.

i. Set CAL-CONTROL unit METER SE-LECT switch to 5000 PRF.

j. Slowly turn PRF control cw on XTALMARK & SYNC unit until meter on CAL-CONTROL unit indicates maximum (approxi-mately 4,500 PRF). The interrogation pulses,on CHANNEL A display, should increase inintensity but not in amplitude. When CAL-CONTROL meter indicates approximately4,500 pps, the amplitude of interrogationpulses should be at the verge of decreasing.

k. If requirements in j above are met, SIDE-LOBE A.O.C. control R328 need not be ad-justed. If requirements are not met, adjustR328 accordingly. (Be careful not to adjustMAIN GATE A.O.C. control R326 by mistake.)

l. Set control unit master control to STBY.

30

m. Disconnect allreceiver-transmitterright-hand panel.

test equipment, removetest panel, and reinstall

n. On receiver-transmitter, clean area ontop of front cover over mode 2 switches andstamp “TEST MOD APPLIED.”88.14. Operational Check

Use Test Set, Transponder AN/APM-123 (V) 1 and the procedures outlined below tocheck the sidelobe-suppression (SLS) capa-bility and the overall performance of the re-ceiver-transmitter.

a. AN/APM-123 (V) 1 Self-Test. Performthe procedures in (1) through (8) below tosee that the AN/APM-123 (V) 1 is functioningnormally.

(1) Connect the equipment as shown infigure 113.12.

(2) Adjust the output voltage of PowerSupply PP-1104A/G to 27.5 volts dc.

(3) Set the C-2714/APX-44 controls andswitches as follows:

Control or switch Position

M a s t e r c o n t r o l - - - - - - - - - - - - - - - - - - - - - - - - - STBYFunction control _______________________ MODMODE 2 ON-OFF switch ______________ ONMODE 3 ON-OFF switch ______________ ONMODE 1 code control __________________ 00MODE 3 code control ------------------ 00AUDIO ON-OFF switch ---------------- OFFI / P s w i t c h - - - - - - - - - - - - - - - - - - - - - - - - - - - - OFF

(4) Allow the equipment to warm up forapproximately 10 minutes.

(5) Set the AN/APM-123 (V) 1 controlsand switches as follows:

Control or switch Position

Power switch __________________________ 115 VACFUNCTION switch - - - - - - - - - - - - - - - - - - - - - SELF

TESTM O D E s w i t c h - - - - - - - - - - - - - - - - - - - - - - - - - 1CODE AB-CD controls _________________ 0000SIDE LOBE SUPPRESSION (ISLS)

SWITCH OFFPRESS TO TEST switch ______________ LOCK

(6) After an approximate 2 minutewarmup period, the white ACCEPTindicator on AN/APM-123(V) 1should light.

(7)

(8)

Rotate the AN/APM-123 (V) 1MODE switch to 2 and then 3/Aand note that ACCEPT indicator re-mains lighted.If the indications in (6) and (7)above are not obtained. the AN/APM-123 (V) 1 is defective and mustbe replaced with one that passes theself-test check.

b. Receiver-Transmitter Test Procedure.(1)

(2)

(3)

(4)

(5)

(6)

(7)

With the equipment connected andcontrols set as in a above, reset theAN/APM-123(V) 1 MODE switch to1 and the FUNCTION switch to SYS-TEM. Note that the red REJECTindicator lights,Set the C-2714/APX-44 master con-trol to NORMAL and note that theAN/APM-123 (V) 1 ACCEPT indica-tor lights.Adjust the AN/APM-123 (V) 1 CODEAB-CD controls to 1000 and note thatthe REJECT indicator lights.Return the CODE AB-CD controls to0000.Repeat the instructions in (2), (3),and (4) above with the AN/APM-123(V) 1 MODE switch first set to 2and then to 3/A.Turn off the C-2714/APX-44 and thereceiver-transmitter. Do not discon-nect the equipment.Remove the right side cover of thereceiver-transmitter by loosening thequarter-turn fasteners and locate thevideo amplifier card (Wilcox part

(8)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

(17)

C 7-TM 11-5895-217-35

No. 116670-2) by referring to figure54, TM 11-5895-217-35.Loosen the holddown screws at eachend of the card and remove the card.Obtain a video amplifier/SLS card(Wilcox part No. 117858-2) and in-sure that it is in good condition.Align the connector of the card withthe receiver-transmitter receptacleand carefully push the card into place.

Caution: Be careful when installingthe video amplifier/SLS card to avoiddamage to connectors, pins, andprinted circuit.Tighten each holddown screw se-curely. Do not overtighten.Reinstall the right side cover of thereceiver-transmitter.Reset the C-2714/APX-44 mastercontrol to STBY, AN/APM-123 (V) 1MODE switch to 1, and FUNCTIONswitch to SYSTEM. Note that theREJECT indicator lights.Repeat the instructions in (2)through (5) above. Reset AN/APM-123 (V) 1 MODE switch to 1.Set the AN/APM-123 (V) 1 SIDELOBE SUPPRESSION (ISLS)switch to ON and note that the RE-JECT indicator lights.Return the SIDE LOBE SUPPRES-SION (ISLS) switch to OFF andnote that ACCEPT indicator lights.Repeat the instructions in (2), (3),and (4) above with the AN/APM-123 (V) 1 MODE switch first set to 2and then to 3/A.

31

Figure 113.11.

C

7-TM

11-5895-217-35

32

Figure 113.12.

C

7-TM

11-5895-217-3533

C7-TM 11-5895-217-35

to 200 ohms.

note:

Figure 113.13. Test and adjustment points for the VIDEOAMPLIFIER/SLS card, physical location diagram.

Page 141, paragraph 95.6 (page 7 of C 1), e. Add the followingchart, Step No. 6, Performance standard Note. Reverse the ohmmeter leads if a resist-

column. Make the following changes: ante between 1,000 and 5,000 ohms is indicated

a. Delete “1 or 2 ohms” and substitute:when the I/P switch is set to MIC.

15 to 75 ohms.Figure 8 (foldout section). After figure 8.

c. Delete “600 ohms” and substitute: 80add figure 8.2.

Figure 8.2. Receiver-transmitter with SLS, block diagram.

(Located in back of change)

34

C7-TM 11-5895-217-35

Figure 49 (foldout section). After figure49.1, add figures 49.2 and 49.3.

Figure 49.2. B+ distribution for RT-494/APX-44with SLS, simplified schematic diagram.

(Located in back of change)

Figure 49.3 B+ distribution for RT-494B/APX-44with SLS, simplified schematic diagram.

(Located in back of change)

Figure 50 (foldout section). Make the fol-lowing changes:

Caption, add: (without SLS).After figure 50, add figure 50.1.

Figure 50.1 Bias distribution for SLS equipment, simplified schematic diagram.

(Located in back of change)

35

Figure 76.1

C7-TM

11-5895-217-35

36

C 7-TM 11-5895-217-35

Figure 119-P1, notes (foldout section). Addthe following:

7. FOR THOSE EQUIPMENTS MODI-FIED BY MWO 11-5895-217-30/4,TWO RED LEADS CONNECTED TOPIN 3 OF J401 HAS BEEN RE-MOVED AND CONNECTED TO PIN10 OF J401, A 4 UF CAPACITOR(14) HAS BEEN CONNECTED BE-

PIN 10 OF J401, A 4 UF CAPACI-TOR (C14) HAS BEEN CON-NECTED BETWEEN A GROUNDLUG AND PIN 3 OF J401, AND A560 OHM RESISTOR (R18) HASBEEN CONNECTED BETWEENPIN 3 AND PIN 10 OF J401.

Figure 123, notes (foldout section). Addthe following:

TWEEN A GROUND LUG AND PIN 6.3 OF J401, AND A 560 OHM RE-SISTOR (R18) HAS BEEN CON-NECTED BETWEEN PIN 3 ANDPIN 10 OF J401.

Figure 119.1-1 (page 18 of C 5 (foldout sec-tion)). Add the following:

NOTE:FOR THOSE EQUIPMENTS MODI-FIED BY MWO 11-5895-217-30/4,

F O R T H E A N / A P X - 4 4 B , THEVALUE OF RESISTOR R234 HASB E E N C H A N G E D F R O M 1,200

OHMS TO 1,000 OHMS, THE VALUEOF RESISTOR R235 HAS BEENCHANGED FROM 68 OHMS TO 200OHMS, AND THE VIDEO OUT TESTPOINT HAS BEEN CONNECTED TOTHE JUNCTION OF RESISTORSR234 AND R235.

TWO RED LEADS CONNECTED Figure 124 (foldout section). After figureTO PIN 3 OF J401 HAS BEEN RE- 124, add figure 124.1.MOVED AND CONNECTED TO

Figure. 124.1 Video amplifier/SLS card, schematic andwave form diagram.

(Located in back of change)

Figure 128 (page 18, C 5), notes (foldout CHANGED FROM 100,000 OHMS TOsection). Add: 22,000 OHMS, RESISTOR R456 HAS

7. FOR THE RT-494B/APX-44, RE- BEEN CHANGED FROM 1.5 MEG-SISTOR R454 HAS BEEN CHANGED OHM T0 330,000 OHMS, AND CA-FROM 33,000 OHMS TO 24,000 PACITORS C451, C454, AND C455OHMS, RESISTOR R455 HAS BEEN HAVE BEEN CHANGED FROM 0.01

UF TO .0047 UFD.

37

C7-TM 11-5895-217-35

By Order of the Secretary of the Army:

HAROLD K. JOHNSON,General, United States Army.

Official: Chief of Staff.KENNETH G. WICKHAM,Major General, United States Army,The Adjutant General.

Distribution:To be distributed in accordance with DA Form 12-36 requirements for direct and generalsupport maintenance literature for the OV-1A; OV-1B; OV-1C U-1A, U-6A, U-8D, RU-8D,U-8F, U-10A, CH-21B; CH-21C, CH-34A, CH-34C, CH-37A, CH-37B, CH-47A, UH-1A;UH-1B; UH-1D, UH-19C and UH-19D aircraft.

NOTES:1. CARD VIEWED FROM FRONT. FRONT IS SIDE ON WHICH PARTS

2 . D E N O T E S P A R T S A N D P I G T A I L S O N F R O N T O F B O A R D .3 . D E N O T E S P R I N T E D C I R C U I T O N B A C K O F B O A R D .

RT-494B/APX-44B, mode one reply code switching card, parts

A R E M O U N T E D .

location and printed wiring diagram.

Figure 87.1.

T M 5 8 9 5 - 2 1 7 - 3 5 - C 5 - 1 8

2 4

33

TM5895-217-35-C5-28

Figure 133.1.

18

TECHNICAL MANUAL

No. 11-5895-217-35

* TM 11-5895-217-35

HEADQUARTERS,DEPARTMENT OF THE ARMY

WASHINGTON 25, D. C., 27 July 1960

CHAPTER 1.Section I.

II.III.IV.

CHAPTER 2.Section I.

II.III.IV.V.

CHAPTER 3.Section I.

II.III.IV.

CHAPTER 4.Section I.

II.III.

CHAPTER 5.

APPENDIX .

GLOSSARY

PREVENTIVE MAINTENANCE INSTRUCTIONSExternal preventive maintenance -----------------------------------------------Removal and replacement -----------------------------------------------------Internal preventive maintenance -----------------------------------------------Periodic functional check

THEORYSystem applicationGeneral theory of transponder setReceiver-decoder theoryEncoder-transmitter theory ---------------------------------------------------Power supply and control circuits theory -----------------------------------------

TROUBLESHOOTINGGeneral troubleshooting techniques ----------------------------------------------Interunit troubleshootingRadar Receiver-Transmitter RT-494/APX-44 troubleshootingReceiver-transmitter trouble isolation ------------------------------------------

REPAIR AND ALINEMENT INSTRUCTIONSRepairsAl inement - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Adjustments

FINAL TESTING - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

REFERENCES

INDEX

FIELD AND DEPOT MAINTENANCE MANUAL

TRANSPONDER SET AN/APX-44

Paragraph

1-34-67-9

10-15

16-2223-2526-3031-3839-46

47-4950-5253-5960-73

74-8485-8889-95

96-114

Page

225

10

1115202157

67707393

119133139

142

148

149

155

*This manual supersedes TM 11-5895-217-35, 27 May 1960.

TAGO 10004A-Aug 1

CHAPTER 1

PREVENTIVE MAINTENANCE INSTRUCTIONS

Section I. EXTERNAL PREVENTIVE MAINTENANCE

1. Scope

a. This manual covers field and depot main-tenance for Transponder Set AN/APX-44. Itincludes instructions appropriate to thirdechelon for preventive maintenance; to thirdand fourth echelons for troubleshooting, repairor replacement of specified parts, alinement,calibration, and test; and to fifth echelon forrebuilding and test. It also lists tools, ma-terials, and test equipment for third, fourth,and fifth echelon maintenance. Detailed func-tions of the transponder set are covered inchapter 2.

b. The complete technical manual for thetransponder set includes TM 11-5895-217-12,TM 11-5895-217-12P, and TM 11-5895-217-35P.

c. For applicable forms and records, refer toparagraph 2 of TM 11-5895-217-12.

d. Forward comments concerning this man-ual to the Commanding Officer, U. S. ArmySignal Materiel Support Agency, Fort Mon-mouth, N. J.

Section II. REMOVAL

4. General

Internal preventive maintenance of the trans-ponder set requires the removal of its compon-ents from the aircraft, and the removal of theircases or covers.

5. Removal

a. Receiver-Transmitter. To remove the re-ceiver-transmitter, proceed as follows:

(1) Disconnect all cables from the frontpanel connectors. The main intercon-necting cable is automatically discon-

2. Periodic Checks

Periodic maintenance procedures and the in-tervals for performing these procedures arelisted in the following table:

Time interval Procedure

Daily External inspection and service (par. 3).200 hours Internal inspection, service, and periodic

pullout bench check (par. 9).200 hours Operational check (in aircraft) with test

equipment (pars. 10-15).

3. External Maintenance

Preventive maintenance is performed to keepequipment in proper working condition, and toprevent or reduce breakdowns and service in-terruptions. Check the following conditions toprevent breakdowns, wear, breakage, corro-sion, dirt, fraying, looseness, overheating, orother indications of abnormal or improper con-dition. Before proceeding, correct any deficien-cies located. For detailed preventive mainte-nance procedures, see TM 11-5895-217-12.

AND REPLACEMENT

(2)

(3)

netted when the receiver-transmitteris withdrawn from its mounting.Loosen the two knurled nuts of theholddown clamps on the mounting byturning them counterclockwise. (Re-fer to TM 11-5895-217-12 for mount-ing illustration.)Turn the knob of the injector-ejectormechanism counterclockwise severalturns. When the receiver-transmitterhas been brought out far enough todisengage the holddown pins, lift thereceiver-transmitter front end slightly

AGO 10004A2

to clear the front panel lip from theinjector-ejector groove. Withdraw thereceiver-transmitter from its mount-ing.

(4) Remove the detachable sideplates byturning the sideplate fasteners oneither plate counterclockwise.

b. Control Unit. The control unit normallyis mounted on the aircraft instrument panel.To remove the control unit, proceed as follows:

(1)

(2)

(3)

Disconnect the main interconnectingcable at the rear of the control unithousing.

Note. In some installations, it may benecessary to remove the control unit beforethe main interconnecting cable can be dis-connected.

Depress and turn each of the fourfasteners on the front panel a quarterof a turn counterclockwise. Withdrawthe control unit from the panel.Remove the wraparound top and sidecover by removing the six screws inthe rear, two at the top, and three ateach side.

c. Mounting. This is a shock-absorbentmounting for the receiver-transmitter. It issecured to the equipment shelf or to the deckby machine screws. To remove the mounting,proceed as follows:

(1)

(2)

(3)

(4)

Remove the receiver-transmitter fromthe mounting (a above).Remove the machine screws in eachresilient mount.Remove the connector assembly at therear of the mounting.Remove the mounting.

d. Antenna. The antenna mounts througha cutout in the aircraft skin. To remove theantenna, proceed as follows:

(1) From inside the aircraft, disconnectthe antenna cable from the antenna.

(2) Remove the six machine screws thathold the antenna in place. (Hold theantenna while removing these screws.)

(3) Withdraw the antenna.e. Fuses. One 10-ampere fuse protects the

transponder set from overload. It is located ina fuseholder on the receiver-transmitter front

AGO 10004A

panel, and it can be removed from outside thecase, A spare fuse is carried in a similar holderabove the in-service fuseholder. To removethese fuses, depress the holder cap and turnit counterclockwise.

f. Cables. The two basic cables are requiredto connect the components of the transponderset. Figure 1 illustrates the cording betweenthe units and the location of the receptacles.Refer to the applicable aircraft technical man-ual for removal of these cables.

6. Replacement

After maintenance, testing, or repair of thecomponents of the transponder set, replace theunits as follows:

a. Antenna.(1) Before replacing the antenna, check

the grounding gasket. This gasket ispart of the antenna and consists of awire mesh imbedded in a flexible gas-ket material. The mesh should beclean and bright, and the gasketshould be free of holes, cracks, andtears.

(2) Place the antenna in position throughthe aircraft skin cutout, and replacethe six machine screws.

(3) Reconnect the antenna cable to the an-tenna receptacle.

b. Mounting.(1) Replace the rear connector of the

mounting.(2) Set the mounting in place on the

equipment shelf and line up the holesfor the mounting screws.

(3) Replace the mounting screws.c. Control Unit.

(1) Attach the main interconnecting cableto receptacle J901 (fig. 1) at the rearof the control unit; be sure that thetwist-lock ring is fully engaged.

Note. In some installations, the controlunit may have to be mounted before attachingthis interconnecting cable.

(2) Set the control unit in place in theinstrument panel opening, and depressand turn each of the four fasteners aquarter of a turn clockwise.

3

TM

5895-217-35-1

Figure 1.

4

d. Receiver-Transmitter.(1)

(2)

(3)

Place the receiver-transmitter be-tween the siderails of the mounting.Slide the receiver-transmitter to the (4)rear until the holddown pins on therear of the mounting engage the guideholes at the rear of the receiver-trans-mitter case. (5)Before the mounting and the case con-

match the lip of the case with thegroove of the injector-ejector mech-anism.Lower the case front, with the lip andgroove engaged. Turn the injector-ejector knob clockwise until the re-ceiver-transmitter case is fully seated.Lock the unit in place by engagingand tightening the holddown clamps

nectors engage, raise the front of thereceiver-transmitter case slightly and

and by turning the knurled nuts clock-wise.

Section III. INTERNAL PREVENTIVE MAINTENANCE

Warning: Dangerous voltages are present inside the receiver-transmitter when power is ap-plied. Be sure that the power is off before attempting any internal preventive maintenancework. Observe safety precautions when making tests or measurements with power applied.

7. General

a. The purpose of preventive maintenance isto locate and correct deficiencies before they leadto malfunction or breakdown. Check for signsof abnormal operation and condition, and takecorrective maintenance action immediately toprevent breakdown or damage.

b. Internal maintenance of the transponderset is carried out at the test bench. The sub-assemblies of the receiver-transmitter are toremain in their proper positions; only the coverplates are to be removed.

8. Internal Maintenance Procedures

Caution: The tube filaments in this trans-ponder are connected in series-parallel. Toavoid possible damage to tubes, be sure thatthe power is off before removing or insertingthe tubes.

a. Remove the receiver-transmitter (par.5a) and the control unit (par. 5b) from the air-craft, and remove the sideplates of the receive-transmitter and the wraparound top and sidecover of the control unit.

b. Follow the procedures listed in the follow-ing chart:

Item Procedure

1 Check internal components for signs of over-heating, breakage, corrosion, damage, deteri-oration, and vibration.

2 Check internal connectors for tightness, cracks,chips, and for good wiring connections.

AGO 10004A

Item

3

4

56

7

8

Procedure

See that printed circuit cards are securely inplace.

Carefully dust interior with cloth or brush, orblow out dust with dry compressed air at notmore than 15 pounds pressure.

Clean the blower opening.Connect 28 vdc power to pin No. 44 and ground

pin No. 22 of J112 (fig. 1).Observe blower operation for quietness and

speed, and tube filaments for lighting,Note. An open filament, in most cases, will cause all

or several of the tubes in a subassembly to remainunlighted.

Disconnect 28-vdc power.

9. Pullout CheckThis check is performed with the receiver-

transmitter and the control unit removed fromthe aircraft and connected to the test equipmentbench test).

a. Test Equipment Required. The test equip-ment required for the pullout check of the trans-ponder set is listed below, with applicable re-ference literature and assigned common names.

Nomenclature Reference

Test Set, Radar AN/ TM 11-1175UPM-6B.

Oscilloscope AN/USM TM 11-6625--81. 219-12

Coder-Decoder GroupAN/UPA-39.

Power Supply PP- TM 11-51261104A/G or equiva-lent.

Headset HS-33 orequivalent.

Common name

IFF simulator.

Oscilloscope.

Coder-decoder.

28-volt supply.

Headset.

5

b. Additional Equipment. Additional equip-ment required for pullout check and their as-signed common names are listed below.

Equipment

UG-565A/U Adapter (1)UG-201/U Adapter (2)Video cable, 10 ft RG-62/U co-

axial cable with two UG-88/Uconnectors.

Interconnecting cable for connect-ing receiver-transmitter to con-trol unit (c below).

Common name

Antenna adapter.Oscilloscope adapter.Video cable.

Bench test cable.

c. Bench Test Setup. The cording, the testequipment connections, and the bench test cableconnections shown in figure 2 illustrate thesetup used to perform the pullout check. Do notconnect the oscilloscope and the coder-decoderuntil actually required because they load theIFF simulator. Fabricate the bench test cableas shown in figure 3. Allow sufficient cablelength ot provide working space and accessi-bility to the units. Fabricate the video cableby installing a UG-88/W connector (fig. 57)on each end of a 10-foot length of RG-62/Ucoaxial cable.

Note. Cables W401, W701, W702, and W703, andadapters E702 and E703 are eupplied with the IFFsimulator. Cables W901, W902, and W903 are suppliedwith the coder-decoder. When setting up the equipmentfor bench test, isolate the coaxial cables as much aspossible to prevent stray pickup.

d. Pullout Check Procedures. Complete thefollowing procedures in conducting a pulloutcheck:

(1)

(2)

Set up the equipment for bench test(c above).Follow the transponder testing proce-dures described in TM 11-1175 to setup the IFF simulator, and check thespecifications listed below. If the cor-rect specifications are not obtained,refer to chapter 3 for corrective main-tenance procedures.

Note. All specifications are taken with27.5 volts ±0.25 direct current (dc) inputmeasured at fuse F101.

Test

Receiver sensitivity (trig-gering or decoding level).

Receiver bandwidth: -------

Receiver center frequency--Receiver LOW sensitivity ___Transmitter power output__Transmitter frequency _____

(3)

Specification

-72 to -76 dbm

6 to 8 mc at 3 db downpoints.

1,030 mc ±1.0-43 dbm ±527 db ±3 db above 1 watt1,090 mc ±1

Connect Oscilloscope AN/USM-81 andCoder-Decoder Group AN/UPA-39 asshown in figure 2, and set the oscillo-scope controls as follows:

Oscilloscope control

MAIN SWEEP:TRIGGERING LEVELSTABILITYTRIGGER SLOPETRIGGERING MODETIME/CMMULTIPLIER

HORIZONTAL DISPLAY

DELAYING SWEEP:TIME/CM or DELAY

TIMEDELAY-TIME MULTI-

PLIER 1-10TRIGGERING LEVELSTABILITY OR EXT.

SWEEP ATTEN.Preamplifier:

MODECHANNEL ACHANNEL B

(4)

Position

Full clockwise.Full clockwise.EXTAC SLOW.10 MICRO SEC.1MAIN SWEEP DE-

LAYED.

2 MICRO SEC.

0

0Set for stable waveform.

CHOPPED.2 VOLTS/CM AC.0.2 VOLTS/CM AC.

Check the codes listed in (5) below;use the coder-decoder to speed identi-fication of pulse positions by matchingthe A, B, C, and D switches with codesselected on the control unit. Comparethe transponder set (CHANNEL A)and the coder-decoder (CHANNEL B)codes presented on the oscilloscope.Set the coder-decoder controls as fol-lows:

6 AGO 10004A

TM

5895-217-35-3

Figure 2.

7

Figure 3.

8

Cader-decoder control Position

S Y N C s w i t c h - - - - - - - - - - - - - - - - - - - - - - - EXTERNALCODE-DECODE switch -------------- DECODEOUTPUT switch - - - - - - - - - - - - - - - - - - - - 2 0 vCODER INT SYNC switch ___________ OFFI/P-NORMAL-EMERGENCY switch NORMAL

(5) Refer to section I of chapter 2 for

additional details of codes, if neces-sary. The code column below refersto types or categories of operation(TM 11-5895-217-12), and the replycolumn refers to reply train pulse out-put (fig. 5) as observed on the oscillo-scope. When operating with the con-trol unit function control in NORMALposition, the coder-decoder will notproduce a comparison code.)

NORMAL:Mode 1Mode 2Mode 3

MOD or CIVIL:Mode 1Mode 2Mode 3

NOMAL-I/P:Mode 1Mode 2Mode 3

MOD-I/P:Mode 1Mode 2Mode 3

CIVIL-I/P :Mode 3

NORMAL-EMER:Mode 1Mode 2Mode 3

MOD or CIVIL-EMER:Mode 1Mode 2Mode 3

(6)

Reply

1 pulse (A, fig. 5)2 pulses, 15.95 usec &O.1 separation (B, fig. 5)1 pulse (C, fig. 5)

Code train 00 to 73 (D through, G, fig. 5)Code train 0000 to 7777 (H through L, fig. 5)Code train 00 to 77 (M through O, fig. 5)

2 pulses, 16 usec *2.5 separation (P, fig. 5) for 30 sec +20 -152 pulses, 16 usec %2.5 separation (Q, fig. 5) for 30 sec +20 -152 pulses, 16 usec &2.5 separation (R, fig. 5) for 30 sec +20 -15

2 code trains spaced 4.35 usec &O.1 (V, fig. 5) for 30 sec +20 -151 code train for 30 usec +20 -15 (X, fig. 5)2 code trains spaced .435 usec &O.1 (Z, fig. 5) for 30 sec +20 -15

1 code train plus 1 pulse 4.35 usec 30.1 after last framing pulse (BB, fig. 5)

4 pulses, 16 usec *2.5 separation (S, fig. 5)4 pulses, 16 usec &2.5 separation (T, fig. 5)4 pulses, 16 usec &2.5 separation (U, fig. 5)

4 code trains spaced 4.35 usec &O.1 (W, fig. 5)1 code train (Y, fig. 5)4 code trains spaced 4.35 usec &O.1 (AA, fig. 5)

Check the transponder set output pulse (b)characteristics as follows: disconnectthe coder-decoder and the video signalfrom CHANNEL A of the oscilloscope.

(c)

Connect the 10 to 1 oscilloscope probeto CHANNEL A and to any of the (d)

three screws in the nylon-insulated endof the transmitting oscillator cavity (7)(cathode V154). Adjust the oscillo-scope to view one pulse only at 0.2usec per centimeter calibration.

(a) Pulse width (50 percent amplitudepoints) 0.45 microseconds (usec)±0.1.

AGO 10004A

Rise time (10 to 90 percent points)less than 0.1 usec.Decay time (90 to 10 percent points)less than 0.2 usec.Amplitude jitter, less than 5 per-cent.

Insert the headset in test jack J2 (fig.3) and listen for noise when the trans-ponder set is not being interrogated.No noise should be heard. Note thefan operation and the general operat-ing conditions.

9

Section IV. PERIODIC

10. General

Functional checks will be made after thetransponder set is installed in the aircraft, andwill be performed every 200 hours. The purposeof the check is to insure that the transponderset functions properly in the aircraft after ithas been serviced and is known to be operatingproperly on the bench.

11. Power Requirements

a. A dc power source capable of maintain-ing 27.5 volts at the full load current drawnby all equipment in the aircraft will be required.Use aircraft ground servicing unit, multipur-pose, type MA-1 or equivalent.

b. A 115-volt, 60 cycles per second (cps)source of at least 500 watts will be required fortest equipment in the aircraft.

12. Test Equipment Required for FunctionalCheck

The following table lists the test equipmentfor functional checks on the transponder set,with applicable reference literature and as-signed common names.

Nomenclature Reference Common name

Test Set, Radar AN/UPM-6B.

Coder-Decoder GroupAN/UPA-39.

Transponder probeantenna.

TM 11-1175 IFF simulator

Coder-decoder

Test hat

13. Functional Check Test Setup

a. The IFF simulator is connected to thetest hat and the antenna, as specified in TM 11-1175, to measure the overall performance. Usethe applicable cable connections shown in figure2.

b. The coder-decoder is used to check all MODcodes. Connect cable W902 from the IFF simu-lator SIF VIDEO OUT MOD IN receptacle tothe coder-decoder VIDEO IN(-) receptacle.

10

FUNCTIONAL CHECK

14. Functional Check Procedures

a. Reply Pulse Characteristic Check. Followthe bench tests given in paragraph 9d (2)take into account the 20 decibel (db) attenua-tion factor of the test hat.

b. Reply Coding Check. Check the codes asinstructed in paragraph 9d (4) to make surethat the aircraft installation wiring is correctNORMAL codes can be observed by measuringthe video with the PEAK VOLTAGE meter onthe IFF simulator in the same manner as emer-gency and identification of position code obser-vations. Identification of position (IP) willproduce a higher meter reading than singlereply trains, and emergency trains a stillgreater increase.

c. Interference Check. Operate the trans-ponder set, while using one of the aircraft head-sets to monitor the audio output. Turn on theother aircraft electronic equipment to makesure that these equipments do not trigger thetransponder set when the IFF simulator attenu-ator is set to -120 decibels referred to 1 volt(dbv). No sound should be audible in the air-craft headset and no output indicated on thePEAK VOLTAGE meter. Interrogate thetransponder set on several modes and codes todetermine that other equipments are not af-fected. Sound should be present in the aircraftheadset used to monitor the transponder setoutput, but not in communication or navigationequipments.

15. Functional Check Conclusion

a. Any malfunctions observed during theabove tests usually indicates a defective an-tenna, coaxial cables, control unit to receiver-transmitter wiring, or dc supply voltage, andmust be corrected before using the aircraftThe units may be bench-checked specifically fora particular fault (par. 9, or ch. 3). Difficultieswith other equipments in the aircraft may in-dicate transponder set troubles or other equip.ment troubles, but they usually indicate a de-fective installation.

b. When satisfactory operation is obtained,disconnect and remove all test equipment. Re-connect any leads that were disconnected dur-ing the above tests.

AGO 10004A

CHAPTER 2

T H E O R Y

Section I. SYSTEM APPLICATION

16. General

a. The transponder set provides transponderfunctions to receive, decode, and reply to thefollowing characteristics interrogations:

(1) Interrogations of Mark X Identifica-tion, Friend or Foe (IFF) System.

(2) Interrogations of Mark X IFF System,supplemented by Selective Identifica-tion Feature (SIF).

(3) Interrogations of the civil secondaryground radar system.

b. TM 11-5895-217-12 includes a functionaldiagram that shows the transponder set beinginterrogated by a ground-based IFF system.

c. Interrogation signals, consisting of pairsof pulses with their spacing governed by theinterrogation mode, are transmitted to thetransponder set by the challenging ground sta-tion. The transponder set decodes the inter-rogation signal pulses and transmits a codedreply to the interrogating station. Replies fromthe transponder set permit positive identifica-tion of nationality and of position, if desired.

d. Coded transponder replies are formed infive operational categories or types. These op-

erational categories are:(1) NORMAL operation.(2) Modified (MOD) operation (also re-

ferred to as SIF).

(3) CIVIL operation.(4) Identification of position (I/P).(5) Emergency (EMER) operation.

e. The working range of the transponder set(limited to line of sight, except for the slightbending effect peculiar to ultra-high frequency(uhf) transmission) depends primarily on theheight of the aircraft.17. Pulse Techniques

a. General. The pulses under discussion in

AGO 10004A

this manual have certain detailed characterics(fig. 4). The terms affiliated with these charac-teristics are defined in the following paragraphs.

b. Pulse Amplitude. Pulse amplitudes aremeasured in average, peak, or peak-to-peakvalues. Average values are determined by not-ing the individual amplitudes at specific timeintervals, and then averaging these values. Peakvalues are measured from the 0-volt base lineto the greatest positive or negative portion ofthe pulse. Peak-to-peak values represent ampli-tude between the maximum positive and nega-tive portions of a pulse.

c. Pulse Width. Pulse widths are measuredat the 50 percent amplitude points of leadingand trailing edges of a pulse. The time distancebetween these points is the pulse width, andis usually expressed in microseconds. The lead-ing edge of the pulse is the left-hand edge asviewed on an oscilloscope that produces a dis-play by left-to-right beam movement.

d. Pulse Rise Time. Pulse rise time is thetime required for the pulse amplitude to risefrom the 10 percent amplitude point to the 90percent point on the leading edge of the pulse.It is usually expressed in tenths of a usec.

e. Pulse Decay Time. Pulse decay time is thetime required for the trailing edge amplitudeto fall from the 90 percent amplitude point tothe 10 percent point. It is usually expressed intenths of a usec.

f. Pulse Separation. Pulse separation, some-times called pulse spacing or pulse interval, isthe time distance between the correspondingpoints on two pulses. It is usually expressed inmicroseconds or parts thereof.

18. Interrogations

a. Three independent interrogation modesare presently in use by military operations:mode 1, mode 2, and mode 3. All three modes

11

Figure 4. Pulse characteristics.

consist of two identical pulses; the differencebetween each of these modes is established bypulse separation. The interrogation pulses havespecific characteristics which permit the trans-ponder set to distinguish between interroga-tions and other pulse groups that may be re-ceived from radars or jamming devices. Trans-mitted interrogation pulses consist of burstsof a radiofrequency (RF) carrier similar tocontinuous wave (cw) code transmissions usedin communication systems.

b. Characteristics of interrogation pulses areas follows:

(1)

(2)(3)(4)(5)

Carrier frequency-1,010 to 1,030megacycles (mc).Rise time-0.2 usec or less.Decay time-0.4 usec or less.Width-0.7 to 1.2 usec.Separation-mode 1; 3 usec (IFFmode). Mode 2; 5 usec (personalidentification mode). Mode 3; 8 usec(flight leader identification mode).

Note. Pulse characteristics apply to thedemodulated RF interrogation pulses as ob-served on an oscilloscope.

c. The interrogation rate or repetition rateis determined by the pulse repetition frequency(prf) of the radar set associated with theground-based IFF system, and may vary be-tween 500 and 2,000 interrogations per second.Interrogations which do not have the character-istics given in b above will be rejected by thetransponder set, and no reply will be trans-mitted.

12

19. Transmitted Repliesa. Transmitted replies consist of bursts of

RF signal (pulses) which have been arrangedwith specific characteristics in time and posi-tion. The type of reply is determined by the in-terrogation mode and the operator code controlselection. Specialized replies are available tothe operator for identification of the position(I/P) and the emergency (EMER) operationsas required by tactical situations. Mode 1 pro-vides 32 code combinations; mode 2 provides4,096 code combinations; and mode 3 provides64 code combinations.

b. The characteristics of the pulses whichmake up the reply codes are as follows:

(1)(2)(3)(4)(5)

Carrier frequency-1,090 to 1,110 mc.Rise time-0.1 usec or less.Decay time-0.2 usec or less.Width-0.451 usec ±0.1.Amplitude variation-10 percent orless.

Note. Pulse characteristics apply to thedemodulated RF reply pulses as observed onan oscilloscope.

c. The combination and separation of pulses,with the characteristics listed in b above, formpredetermined coded reply trains which are re-ceived by the ground-based IFF system. Theground equipment uses a go-no-go decoder sys-tem to make sure that the received coded replytrain is according to tactical orders.

20. Reply Coding by Categorya. General. Several typical reply codes are

AGO 10004A

shown in figure 5. These sample replies indicatepulse position and pulse identification with re-spect to the interrogation mode and the selectedand assigned reply codes. The reply codes inA through O represent typical replies obtainedwith the master control in the NORM (or LOW)position. These replies include the basic singlereply trains for each interrogation made withdifferent operational categories and selectedcodes. The reply codes in P through BB are therepeated replies obtained in I/P or EMER. Thefollowing paragraphs discuss the pulses andtheir identification by operational category(par. 16d). The technician must thoroughlyunderstand the composition of a coded replytrain before attempting maintenance proce-dures.

b. NORMAL Reply Codes. In a conventionalMark X IFF system, the transponder set ischallenged by a pulse pair that has one of threespacings between pulses: three usec, five usec,or eight usec, representing modes 1, 2, and 3,respectively. The transponder set, operatingin the NORMAL category (function control atNORMAL), replies with a code of one (modes1, 3), two (mode 2), or four (emergency)pulses. In A, B, C (fig. 5), the initial replypulse shifts to the right because the zero timebase used throughout figure 5 is obtained fromthe second pulse of an interrogation pulse pairof mode 1. Reply pulse characteristics arespecified in paragraph 19b.

c. MOD (SIF) Reply Codes. As in the caseof NORMAL operation, the Mark X IFF chal-lenges to SIF-equipped transponder sets consistof a pulse pair with three-, five-, or eight-usecspacing, depending on the interrogation mode.The transponder set reply is a coded pulse trainwith a number of selectable codes for each replymode. The makeup of this pulse train, in gen-eral terms, is as follows:

(1)

(2)

Two framing pulses, spaced 20.3 usec ±0.05, are always present in SIF re-plies for any interrogation mode orreply code selection (D, fig. 5).From 1 to 12 pulses, between thesetwo framing pulses, are present forcoded identification. These pulses aredivided into two groups, each contain-ing up to six pulses. Spacing betweenthese two groups is fixed at 2.9 usec.

AGO 10004A

Spacing between pulses within eithergroup is 1.45 usec or 2.9 usec, depend-ing on code selection and reply mode.The 1.45 usec spacing is involved onlyin mode 2 replies (J, L, fig. 5).

d. CIVIL Reply Codes. CIVIL interrogations,also consisting of a pulse pair with 3-, 5-, or 8-usec spacing, depending on the mode, providethe necessary overlap between CIVIL and IFFsystems for compatibility. Replies in CIVILfunction setting are identical with those inMOD function setting, except for the CIVILI/P reply. This reply coding is illustrated inBB, figure 5.

e. Identification of Position Reply Codes. Inall cases, if the ip coding is inserted, the ipreply code is displayed for 30 seconds + 20-15when continuously interrogated. With thefunction switch set to NORMAL, ip replies con-sist of two pulses. This is a sustained displayof two reply pulses for each interrogation, nota repetition of pulses. In the MOD-I/P functionsetting, mode 1 and mode 3, replies consist oftwo selected reply trains (the original trainand one repetition) with a spacing betweenthe two reply trains of 4.35 usec ±0.1. Mode2 ip replies are not changed for this function,but remain the same as the standard reply.CIVIL-I/P replies (BB, fig. 5) include theselected reply train, with one pulse added, 4.35usec *0.1, after the last framing pulse. Thisreply train is not repeated but will be presentfor each interrogation received. Repeated re-plies in MOD, modes 1 and 3 only, produce twocomplete reply trains for each interrogation.All ip functions are sustained for 30 seconds+ 20 -15 by the time delay switch to providesufficient time for performing tactical duties.

f. Emergency (EMER) Reply Codes. Withthe EMER control setting and the NORMALfunction selection, the reply consists of fourpulses, 16 usec ±2.6 apart, in any of the threemodes (S, T, U, fig. 5). In the MOD or CIVILfunction, the EMER reply to mode 1 and mode3 interrogations will be the selected reply code,displayed four times for each interrogation(W, AA, fig. 5). The mode 2 reply is the MODor CIVIL function will be the normal mode 2reply (Y, fig. 5).

13

21. Reply Coding by Assigned Code Numbera. Assigned Code Number. For tactical pur-

poses, IFF code assignments are changed fromtime to time. These codes consist of 2- or 4-digit numbers which indicate the correct set-tings of code controls or switches. The trans-ponder set converts this, code to a coded pulsetrain. For modes 1 and 3, the assigned codenumbers are 2-digit numbers. For mode 2, theassigned code number is a 4-digit number.

b. Code Group Letter. The pulse train forSIF consists of two framing pulses and up to12 information pulses for mode 2, or up to sixinformation pulses for modes 1 and 3. The 12information pulses (mode 2) are divided intofour groups of three pulses, and each group ofthree pulses is identified by a code group letter.The code group letters are A, B, C, and D. Thesecode group letters always apply to the samethree pulses, and, in combination with the pulseposition number (c below), permanently iden-tify each of the information pulses (fig. 5). Thedigits of the assigned code number (a above)indicate the code group to be used and the pulsecoding within that group. In a 4-digit number,the first digit (thousands) designates the Agroup coding; the second digit (hundreds), theB group coding; the third digit (tens), the Cgroup coding; and the fourth digit (units),the D group coding. In the 2-digit assigned codenumber (modes 1 and 3), only the A and Bgroups are used to represent tens and units,respectively.

c. Pulse Position Number. Positive identifi-cation of pulses within a group is accomplishedby assigning a number to each pulse in a group.The numbers used are 1, 2, and 4, and they areassigned to the pulses of each group in sequence.Hence, there is an A1, A2, and A4, a B1, B2,and B4, and so on.

(1)

(2)

These numbers were used because theirvarious sums give the maximum num-ber of combinations, without repeti-tion, for three numbers. By usingvarious combinations of these numbersany digit from zero to seven can beobtained.The code number for each group is adigit from zero to seven. This codenumber is set up in the code switching

system to provide pulse position num-bers whose sum is equal to the desiredcode number for that code group. Thefollowing example will clarify this:

Code number 5610

Codeletter

ABCD

Codenumber

5610

Pulses in reply code

Pulses A1 and A4 (1 + 4 = 5)Pulses B2 and B4 (2 + 4 = 6)Pulse C1 = 1No pulses = 0

(3) The foregoing example shows the setupfor mode 2 reply coding. Mode 1 andmode 3 codes are readable directlyfrom their code controls. However,the combination of pulses in modes 1and 3 is made up in the same way,using only two digits.

22. Mode 2 Switching ArrangementSwitches for setting up the mode 2 replay

code are located on the receiver-transmitterfront panel (fig. 6). They are enclosed by asmall door on the front-cover left side.

a. The 12 mode 2 code switches are arrangedin four horizontal rows with three switches ineach row. They are numbered from left toright and from top to bottom, with numerals1 through 12.

b. The four rows correspond to the four pulsegroups (A, B, C, and D), and the three switchesin each row correspond to the pulse positionnumbers (1, 2, and 4) within the pulse group.This explanation is simplified in the followingchart.

Switch No. Pulse group Pulse position No.

123456789

101112

AAABBBCCCDDD

124124124124

AGO 10004A14

c. Mode 2 code assignment is given by a 4-digit number. The digits represent pulse groupletters and the digit numeral represents thesum of the pulse position numbers.

Example: Code number 5610 would requireswitches No. 1, 3, 5, 6, and 7 to be at ON, withall others at OFF. The left-hand digit of the

code number being 5 calls for the A group pulsesin positions No. 1 and 4, because only thesetwo position numbers have a sum total of 5.Switch No. 1 controls pulse A1; switch No. 3,pulse A4; switch No. 5, pulse B2; switch No. 6,pulse B4; and switch No. 7, pulse C1. No Dgroup pulses are required in code 5610.

Figure 6. Receiver-transmitter, front panel.

Section II. GENERAL THEORY OF TRANSPONDER SET

23. Interrogation Signal Paths(fig. 7)

a. The transponder set receives all interroga-tions through Antenna AT-884/APX44. Theantenna receives and transmits horizontallypolarized signals in all directions. The receivedsignal frequency is 1,030 mc. Interrogationsreceived by the antenna are fed through theduplexer to the receiver section of RadarReceiver-Transmiter RT-494/APX-44. Theduplexer allows the transponder set to receiveand transmit with the same antenna, withoutusing mechanical switching parts. This reduceslosses in signal power and changeover time. Thereceiver is a superheterodyne type having

AGO 10004A

broadband characteristics to accommodate RFpulses without distortion. Its sensitivity is con-trolled by the NORM and LOW positions of themaster control in the Transponder Set ControlC-2714/APX-44, and also by automaticallysensing the interrogation rate. The video pulsesfrom the receiver have had all undesirablepulses eliminated, such as pulses of unequalamplitude, too narrow in width, or spaced lessthan 2 usec after the first pulse. The videopulses from the receiver consist of a pulse pairfor each interrogation; the time between thepulses of a pair will be either 3, 5, or 8 usec,depending on the interrogation mode.

b. The video from the receiver, in the form

15

of interrogation pulse pairs, is applied to thedecoder which performs the following functions:

(1)

(2)

(3)

(4)

Determines whether a proper interro-gation has been received.Determines the received signal’s in-terrogation mode.Generates mode-sensing gate pulsesthat enable the mode sensitivity en-coder circuits to accept a selected replytrain of pulses.Generates main gate pulses to blankout all interrogations for a period of120 microseconds after a receivedpulse pair (which allows time to com-plete a reply and avoids multiple re-plies), and to synchronize encoder re-ply train construction.

24. Reply Signal Path(fig. 7)

a. When a main gate pulse is received, theencoder is triggered and starts building up atrain of pulses. The operational switching cir-cuits of the control unit select the desired replycodes that will be assembled within the encoder.Whenever an interrogation is received, the en-coder assembles a mode 1, 2, and 3 reply train.The mode-sensing gate pulse from the decodercauses the encoder to pass a correct reply train,according to the interrogation mode. Functionalcontrols in the control unit determine whetherthe encoder shall produce a coded reply for nor-mal, modified (SIF), or civil IFF system, andwhether the reply is to be a normal (NORM),identification of position (I/P), or emergency(EMER) tactical reply. When all control unitswitches are at ON, the decoder mode-sensinggate pulse permits only the reply determined bythe interrogation mode to be passed to the modu-lator-transmitter stages, although a code is de-veloped for replies in all three modes.

b. The coded reply train received by themodulator-transmitter section is amplified con-siderably through the modulator portion. Thisamplification is necessary to provide high ampli-tude pulses for the transmitter. These pulsesactually supply plate power to the transmittingoscillator. Thus, whenever a pulse occurs, thetransmitter generates an RF carrier for theduration of the pulse. The standby (STBY)

16

position on the control unit function switch pre-vents the encoder from triggering the modula-tor-transmitter when it is not desirable to replyto an interrogation for tactical reasons.

c. The RF reply pulses from the transmitterare applied to the duplexer. The duplexer pre-vents these pulses from entering the receiver,and passes them to the antenna. The antennaradiates the RF reply pulses in a horizontallypolarized, omnidirectional pattern. The peakpower output of these pulses is approximately500 watts.

d. Transponder Set Control C-2714/APX-44is divided into two basic sections, functional andoperational switching. Functional switching ap-plies power to the tube filaments, operatespower relay K5 which applies input power tothe high- and low-voltage power supplies, andsupplies power for relay operation, mode, andcategory (NORMAL, MOD, CIVIL, I/P, orEMER) circuits. Operational switching presetsand controls the reply codes according to thetactical requirements, by operating applicablecircuits in the decoder and encoder.

25. Block Diagram Analysis of Receiver-Trans-mitter

Radar Receiver-Transmitter RT-494/APX-44 signal paths are shown in figure 8. and arediscussed in a through k below. Circuit detailsof each card, subchassis, and stage are includedin paragraphs 26 through 46.

a. ANTENNA receptacle J101 connects tothe duplexer in the receiver-transmitter. Theduplexer allows transmitting and receiving witha common antenna system. Duplexer coaxialcable sections are resonant for signal rejectionand nonresonant for signal transmission. Thecoaxial cable sections of the duplexer arearranged so that the receiver cable section is anopen circuit at the transmitter frequency, andthe transmitter cable section is an open circuitat the receiver frequencies.

b. RF interrogation pulses at a carrier fre-quency of 1,030 mc are fed through two pre-selector cavities (Z101 and Z102) to mixer diodeCR102. Oscillator V101A, using quartz crystalY101, generates a signal of 90.83333 mc whichis applied to tripler V101B. The output oftripler V101B at 272.4999 mc. is fed to harmonic

AGO 10004A

Figure 7. Transponder set, block diagram.

generator CR101 which produces many har-monics in its output. Harmonic selector cavityZ103 selects the fourth harmonic (1,090-mc)and applies that frequency to mixer CR102. Themixer beats the 1,090-mc signal with the re-ceived 1,030-mc interrogation pulses. The out-put of mixer CR102, consisting of 60 mc (differ-ence frequency), is connected to the intermedi-ate frequency (IF) amplifiers.

Note. The preselector mixer cavity consists of twopreselector cavities (Z101 and Z102) and one harmonicselector cavity (Z103).

AGO 10004A

c. Six stagger-tuned IF amplifier stages(V201 through V206) amplify the 60-mc outputof mixer CR102. During low signal input con-ditions, these amplifiers operate as conventionalamplifiers with pickoff detector CR203 acting asthe second detector. As signal strength in-creases, IF amplifiers V204, V205, and V206begin limiting, and pickoff detectors CR201 andCR202 begin to operate. This detection systemprovides a linear video output variation fromthe IF detector circuit as the signal input levelto the receiver is varied logarithmically. This

17

is required to assist the suppressor (d below) toeliminate received pulses of unequal amplitude.Automatic Overload Control (A.O.C.) from theA.O.C. amplifier and rectifier is applied to IFamplifiers V202, V203, and V204. This controlsthe receiver sensitivity according to the interro-gation rate instead of the signal strength. Wheninterrogations from several ground stations arereceived, resulting in a high interrogation rate,the receiver sensitivity is decreased so that thetransponder set will reply to strong signals only.

d. First video amplifier and cathode followerV207 provide video pulse amplification andmatch impedance to the input of the suppressorcircuit (diodes CR204 through CR207). Theamplitude of the two pulses of a given inter-rogation pulse pair will be almost equal. Straypulses or additional interrogations from othersources will usually differ in amplitude from thegiven interrogation pulse pair. This differencein amplitude is used in the suppressor to elimi-nate random transponder triggering. The ampli-tude of the first pulse establishes the operatingof reference level of the suppressor. The sup-pressor eliminates any pulses following the firstpulse by 2 microseconds or less, or having anamplitude of 10 db or more below that of thefirst pulse. The suppressor also maintains theinput to second video amplifier and cathode fol-lower V208 at a constant level. The second videoamplifier and cathode follower amplifies thevideo pulses and lowers the circuit impedance tomatch the input to V301. The positive pulsesfrom V208 are amplified and applied to thefront-panel RCVR OUT receptacle J104 andspike suppressor V301.

e. Spike suppressor V301 eliminates pulsesof 0.3 usec or less in width and decreases thewidth of each interrogation pulse by 0.3 usec.This eliminates most of the received noisepulses. Inverter and blanked cathode followerV302 receives interrogation pulses from thespike suppressor output and a main gate pulsefrom blanking cathode follower and amplifierV303. The interrogation pulses from V302 areapplied to all three decoders (V351, V352, andV353). When one of the decoders receives itscorrect code and mode, main gate multivibratorV404 is triggered.

f. Each decoder (V351, V352, and V353)identifies and passes only its assigned interroga-

tion mode pulse pair. All decoder outputs aresingle pulses, 0.4 usec in width, and are used totrigger circuits that begin the assembly of areply train.

(1) The negative pulse output of each modedecoder triggers its respective modegate multivibrator (V401, V402, andV403). The gate pulse from a modegate multivibrator is applied to thecorresponding mode reply selector(V451, V452, and V453,) allowing itto operate. Because only one interro-gation is fed to the decoders, only onedecoder will pass a pulse to its modegate multivibrator; therefore, only onemode reply selector will form a replytrain.

(2) Main gate multivibrator V404, themain synchronization generator, re-ceives a decoder output pulse from anymode through a common decoder out-put connection. This common decoderoutput is also applied to the mode 1gate multivibrator V401 and the ringaround gate multivibrator V503 whenthe switching diode CR354 is closed.When operating in the NORMAL cate-gory, either I/P or EMER, diodeCR354 is closed and mode 2 and 3 replyselectors (V452 and V453) are dis-abled. This develops a mode 1 normalreply for a mode 1, 2, or 3 interroga-tion.

(3) The negative main gate pulse fromV404 is amplified by main gate ampli-fier V454A, and applied to blankingcathode follower and amplifier V303.The output of V303 cuts off theblanked cathode follower portion ofV302. This prevents any interrogationthat is less than 120 usec after the firstpair from triggering the transponderset. The blanking gate from V303 isalso applied to the automatic overloadcontrol A.O.C. amplifier V304 and theSUPPR jack J106. The blanking gateis amplified and rectified by the A.O.C.system. The A.O.C. output bias con-trols the receiver sensitivity by chang-ing the bias on IF amplifiers V202,V203, and V204. This bias voltage is

18 AGO 10004A

(4)

(5)

governed by the interrogation repeti-tion rate, and prevents the excessivetransmitter duty cycle that would re-sult if the transponder set replied toall interrogations. The negative maingate from V404 is also applied to theringing oscillator and driver V551,which generates a ringing oscillatoroutput for each decoded interrogation.A positive main gate pulse from V404is applied to the trigger amplifier andencoder blocking oscillator V501. TubeV501 supplies a 1-usec pulse to delayline DL601. This 1-usec pulse appearsas numerous accurately timed pulsesavailable at the output taps on DL601.Each mode reply code switching cardselects the desired pulses from thedelay line according to its code selec-tion and assembles them as a train ofpulses.During MOD and CIVIL emergency,and MOD identification of position op-erations, switching diodes CR355 andCR356 are closed, causing mode 1 de-coder V353 and mode 3 decoder V351to trigger ring around gate multivibra-tor V503. Because mode 2 interroga-tions do not require repeated replies,ring around gate multivibrator V503is not used to repeat the basic replytrain.

g. The three identical mode reply selectors(V451, V452, and V453) accer’ “* reply codetrain assembled by their respective reply codeswitching cards. The one reply code passed toreply train amplifier V454B is determined byinterrogation mode and the mode gate genera-tors. If a mode 3 interrogation is received andno special reply is required, the positive mode3 gate from V403 will allow reply selector V453to pass the selected mode 3 reply code train.The negative pulse train output from any of thereply selectors is amplified in reply train ampli-fier V454B, and fed as positive pulses to coin-cidence detector V554.

h. A negative main gate pulse excites ringingoscillator V551 and allows it to oscillate atapproximately 690 kilocycles (kc) providingaccurate 1-cycle periods of 1.45 usec. This sig-nal provides accurate timing of reply train pulse

AGO 10004A

separation. First and second clippers V552 clipboth positive and negative peaks to obtain sym-metrical square waves that have a constantamplitude during the entire main gate pulseperiod. Differentiator V553A, a video peakingamplifier, drives coincidence detector V554.Each of the reply code train pulses from replytrain amplifier V454B allows coincidence detec-tor V554 to pass one ringing oscillator positivehalf cycle. Output pulses of V554 are accuratelyspaced because of the ringing oscillator accu-racy, and coded by the pulses of the mode replycode switching cards. The output from V554triggers blocking oscillator V553B.

i. The output of blocking oscillator V553B isapplied to trigger amplifier and blocking oscil-lator V151. The two blocking oscillators (V553Band V151) provide pulses with a very fast riseand decay time, and constant amplitude. DriverV152 amplifies the reply train pulses from V151to provide sufficient drive for modulator V153.The high positive pulses from V153 are appliedto transmitting oscillator V154. These highamplitude pulses (approximately 2,000 volts)provide plate voltage for oscillator V154, allow-ing V154 to oscillate whenever a pulse occurs.Transmitting oscillator V154 oscillates for peri-ods of approximately 0.45 usec, at a frequencyof 1,090 mc. The separation between periods ofoscillation is determined by the selected replycode train. The output RF reply train is con-nected through the duplexer to antenna recepta-cle J101 for application to the antenna.

j. Ring around gate multivibrator V503 pro-vides the repeat characteristics required foremergency and identification of position replies.Tube V503 is triggered by either an all-modedecoder pulse from switching diode CR354, ora mode 1 or 3 decoder pulse from switchingdiodes CR355 and CR356. In the civil category,all three switching diodes are open, and ringaround gate multivibrator V503 does not oper-ate. In MOD (SIF) emergency and identifica-tion of position functions, diode CR354 is openand diodes VR355 and CR356 are closed. Thisallows ring around gate multivibrator V503 tooperate for modes 1 and 3 but not for mode 2interrogations. The width of the ring aroundgate multivibrator pulses is adjusted accordingto the reply train repeat time requirements.Ring around gate pulse widths are as follows:

19

37 usec for MOD-I/P modes 1 and 3, 57 usecfor NORMAL emergency, and 87-usec in MODemergency modes 1 and 3. The positive ringaround gate pulse is applied to gated amplifierV502.

k. The selected ring around gate pulse allowsgated amplifier V502 to amplify pulses from thering around bus in mode 1 reply code switchingcard. In the normal categories (except identifi-cation of position), a 15.05-usec pulse is appliedto tube V502. In the modified and civil cate-gories, a 23.85-usec pulse is applied to V502.These pulses appear to be approximately 0.9usec short to produce the required spacing be-tween repeated reply trains; this shortage ismade up in the input delay of delay line DL601and miscellaneous circuit delays. Each time aring around pulse from the mode 1 code switch-ing card ring around bus is received, and a ring

around gate (from V503) is present, gatedamplifier V502 will trigger encoder blockingoscillator V501 and excite delay line DL601.

l. All power for the receiver-transmitter isobtained from the 27.5-volt dc source. Twotransistorized power supplies change 27.5 voltsdc to obtain the voltages required throughoutthe receiver-transmitter. The low-voltage powersupply, consisting of transistor Q1 and Q2 withsilicon diodes CR1 through CR8, supplies thefollowing voltages: +125 volts dc, for most ofthe tube plate circuits; -150 volts dc, for biasrequirements; and 115 volts ac to operate blowerB1. The high-voltage power supply, consistingof transistors Q3 and Q4 with silicon diodesCR9 through CR24, produces +300, +600, and+1,200 volts dc for modulator-transmitter re-quirements, and 6 volts ac for the transmittingoscillator V154 filament.

Section III. RECEIVER-DECODER THEORY

26. Converter Subchassisa. General (fig. 9). The converter subchassis

changes the 1,010- to 1,030-mc interrogationpulses to an IF of 60 mc. It consists of the pre-selector mixer cavity unit (including threetuned cavities), two diodes, one tube, and asso-ciated circuit components. Crystal oscillatorV101A generates a signal of predetermined fre-quency between 89.16 and 90.83 mc. TriplerV101B selects the third harmonic of the crystaloscillator output (between 267.5 mc and 272.49mc) and applies it to harmonic generatorCR101. Harmonic generator CR101 passes thetripler output and many harmonics to harmonicselector cavity Z103. Cavity Z103 is tunablefrom 1,070 to 1,090 mc. It selects the fourthharmonic of the tripler output frequency andapplies it to mixer CR102. The received RFinterrogation pulses picked up by the antennaare applied to the duplexer. The duplexer passesthe received pulses to preselector cavity Z101,and prevents signals from the transmitter sec-tion from entering the receiver. The output ofZ101 is applied to Z102. Both preselector cav-ities Z101 and Z102 are tuned to the receivedsignal frequency within the range of 1,010 and1,030 mc. The output from Z102 is applied tomixer CR102. Mixer CR102 heterodynes thetwo signals and passes the difference frequency

20

to the IF suppressor subchassis. The IF outputfrom the converter subchassis consists of 60-mcinterrogation pulses.

b. Preselector (fig. 10). The received RFinterrogation pulses from the duplexer con-nected to jack J102 are loop-coupled into pre-selector cavity Z101. Both cavities Z101 andZ102 are tuned to the received signal frequency1,030 mc. The signals pass from Z101 to Z102through the slot in the wall between the twocavities. The output from Z102 is loop-coupledfrom the cavity, and applied through couplingcapacitor C108 to mixer CR102.

c. Crystal Oscillator (fig. 10). Crystal oscil-lator V101A uses a Pierce oscillator circuit,with crystal Y101 operated above dc ground(plate voltage across the crystal). Plate voltageis supplied from the +300-volt dc distributionbus (par. 41d) through two decoupling filters(R105, C104 and R104, C103) through plate-load resistor R103 and plate inductor L101. In-ductor L101 is tuned to the crystal frequency of90.83333 mc. Capacitor C102 reduces the ampli-tude of the feedback to the proper level. Re-sistor R101 and capacitor C101 develop gridleak bias when the oscillations cause the grid todraw current, and R102 prevents parasitic oscil-lations. Filament voltage is supplied directlyfrom the +27.5-volt dc source through filament-dropping resistor R109 and bypassed with C109.

AGO 10004A

Figure 9. Converter subchassis, block diagram.

d. Tripler (fig. 10). Theoutputfrom V101Ais coupled through C106 to the grid of triplerV101B. Tripler V101B is maintained near cut-off with bias obtained from the -150-volt dcbus (par. 42) and a voltage divider networkconsisting of dropping resistor R107 and gridresistor R106. This bias causes nonlinear oper-ation of V101B which generates harmonics, aid-ing frequency multiplication. Capacitor C105prevents feedback into the -150-volt dc bus.Plate voltage is obtained from the +300-volt dcbus (par. 41c) through decoupling filter R104and C104 and the plate inductor L102. InductorL102 is tuned to the oscillator’s third harmonicat approximately 272.49 mc. The output fromV101B is coupled through C107 and developedacross R108, the input resistor, for the har-monic generator.

e. Harmonic Generator and Selector (fig. 10).The tripler output is applied to the cathode ofharmonic generator CR101. Because a diode isa nonlinear device, it is capable of developingmany harmonics of any signal applied to it. Theoutput of CR101 is loop-coupled into the har-monic selector cavity Z103. This output consistsof the output frequency of V101B with many ofits harmonics. Harmonic selector cavity Z103is. tuned to the fourth harmonic of the tripleroutput frequency. This harmonic frequency atapproximately 1,090 mc is loop-coupled out of

AGO 10004A

the harmonic selector and applied directly tomixer CR102.

f. Mixer (fig. 10). The 1,090-mc signal fromharmonic selector Z103 and the 1,030-mc RFinterrogation pulses from preselector cavityZ102 are both applied to the cathode of crystalmixer CR102. These two signals are hetero-dyned at the mixer, The signals present at theoutput of the mixer include the two funda-mental frequencies, their sum, their difference,and several harmonics. Capacitor C110 by-passes all of the unwanted frequencies andallows only the 60-mc difference frequency topass. This output, consisting of 60-mc RF in-terrogation pulses, is connected to the IF sup-pressor subchassis through a coaxial cable andplug P101.

27. IF Suppressor Subchassis(fig. 11)

a. General. The 60-mc interrogation pulsesfrom mixer CR102 are amplified by six stagger-tuned, transformer-coupled IF amplifiers (V201through V206) operating as conventional ampli-fiers on low input signal levels. During lowinput signal conditions, third pickoff detectorCR203 operates as the detector, converting the60-mc pulses to video pulses. As the input signallevel increases, sixth IF amplifier V206 beginsto act as a limiter and infinite impedance detec-

21

Figure 10.

22

TM

5895-217-35-9

Figure 11.

23

tor in conjunction with second pickoff detectorCR202. Further signal increase causes fifth IFamplifier V205 and CR201 to react in the samemanner as that of the sixth IF stage. Circuitconstants are such that as a diode approachessaturation, the amplifier preceding that diodebegins to limit, and detection with the precedingdiode occurs. All three pickoff detectors feedvideo pulses to a common video output. Thethree pickoff diode outputs are in phase and areapplied to first video amplifier V207A as posi-tive pulses. IF amplifier V204 limits on ex-tremely strong signals to keep the video pulseinput to tube V207A within operating limits.High or low sensitivity (selected by the mastercontrol on the control unit) is applied to thefirst and second IF stages, while automatic over-load control (A.O.C.) is applied to the second,third, and fourth stages. A.O.C. consists of anegative bias obtained by amplifying and recti-fying the main gate multivibrator pulses. Thisbias prevents excessive transmitter duty cyclewhen more than one interrogating station is re-ceived. First video amplifier and cathode fol-lower V207 amplifies and lowers circuit imped-ance to match the input to suppressor CR204through CR207. The suppressor removes anypulse occurring less than 2 microseconds afterthe first pulse, or having an amplitude of 10-dbor more, lower than the first pulse. All otherpulses with less than 10-db amplitude differenceare applied to second video amplifier V208Awhere they are amplified and passed to cathodefollower V208B for impedance matching. Videopulse output is fed to front panel RCVR OUTjack J104 and the video amplifier card.

b. First and Second IF Amplifiers (fig. 12).The 60-mc input from jack J201 is applied tothe tap on transformer T201. TransformerT201 provides the proper impedance match be-tween the coaxial cable and the first IF tubeinput. Transformer T201 is tuned to approxi-mately 60 mc as determined by the best overallfrequency response. Jack J202, in series withT201 ground return, permits measurement ofmixer CR102 current, and capacitor C250 filtersRF from the meter. Resistor R201 shunts T201to broaden its frequency response. First IF am-plifier V201 obtains plate voltage from the +125-volt dc distribution bus (par. 41e) through thedecoupling filter, consisting of R204 and C202,

and the primary of transformer T202 shuntedby resistor R203. Resistor R203 broadens thetransformer frequency response. TransformerT202, tuned to approximately 63 mc, couples theoutput of V201 to the grid of second IF ampli-fier V202. Screen grid voltage is taken fromthe plate-decoupling filter and applied throughisolation resistor R243. Resistor R202 and HISENS control R225, bypassed by C201, providecathode bias for first IF amplifier V201. Re-sistor R205, bypassed by C206, provides cathodebias for second IF amplifier V202. LO SENScontrol R226, bypassed by C230, provides addi-tional bias for both V201 and V202. Variableresistors R225 and R226 are adjusted to providethe desired receiver sensitivity for the LOWand NORM positions of the master control onthe control unit. Pin No. 7 of J203 is groundedin the NORM position; therefore only R225 iseffective and must be adjusted first; R226 isthen adjusted for proper LOW sensitivity. Inaddition to the cathode bias, A.O.C. bias isapplied to grid of tube V202 through filter net-work L201, C203, and C205. At low signal levels,the A.O.C. bias voltage is slightly positive, par-tially reducing the effect of the cathode bias.Plate voltage for V202 is supplied from the+125-volt dc distribution bus (par. 41e)through the decoupling filter, consisting ofR206 and C207, and the primary of transformerT203 shunted by resistor R207. Isolating re-sistor R244 connects screen grid voltage fromthe decoupling filter.

c. Third and Fourth IF Amplifiers (fig. 13).Transformer T203, tuned to approximately 57mc, couples the input to third IF amplifier V203.Bias is provided by cathode resistor R208 andbypass capacitor C210. A.O.C. bias is appliedto the grid through inductor L203, bypassed bycapacitor C209. Plate voltage is supplied by the+125-volt dc distribution bus (par. 41e)through the decoupling filter consisting of R210and C211, and the primary of transformerT204 shunted by resistor R209. Resistor R209broadens the transformer frequency response.Screen grid voltage is applied from the decou-pling filter through isolation resistor R245.Transformer T204, tuned to approximately 63mc, couples the signal output to the grid offourth IF amplifier V204. Bias for V204 isobtained from cathode resistor R211 and bypass

24 AGO 10004A

25

Figure 13.

Figure 12. First and second IF amplifiers, partial schematic diagram.

capacitor C214. A.O.C. bias is applied to thegrid through inductor L205, bypassed by ca-pacitor C213. Resistor R242 and diode CR209provide the positive grid bias on the A.O.C. bus.Current flow from ground through CR209 andR242 to +125 volts dc, places the diode anodeand A.O.C. bus at approximately +0.5 volt dc,if no negative input voltage is applied to pinNo. 4 of receptacle J203. The negative A.O.C.voltage from the video amplifier card reducesthe receiver sensitivity. This voltage is the re-sult of sensing the interrogation rate, using themain gate pulses. The purpose of the A.O.C.bias is to reduce the rate of transponder repliesto a level that will not damage the transmitter.Plate voltage for tube V204 is obtained fromthe +125-volt dc distribution bus (par. 41e)through decoupling filter R213 and C215, andthe primary of transformer T205, shunted byresistor R212 which broadens transformer fre-quency response. Screen grid voltage is suppliedfrom the decoupling filter through isolating re-sistor R246.

d. Fifth and Sixth IF Amplifiers (fig. 14).Transformer T205, tuned to approximately 57mc, couples the signal from V204 to fifth IFamplifier V205. The fifth and sixth IF ampli-fiers perform several functions directly relatedto signal strength. In addition to normal IFamplification of weak signals, limiter action anddetection takes place in both tubes on strongsignals. The detector pickoff diodes (CR201,CR202, and CR203) couple the video pulses toa common output.

(1) The input signal is coupled throughtransformer T205 to the grid of fifthIF amplifier V205. At low signallevels, it is amplified and coupledthrough transformer T206, tuned toapproximately 63 mc, to the grid ofsixth IF amplifier V206. Higher-than-usual cathode bias is developed acrossresistor R214 and capacitor C220 fortube V205, and across R220 and C223for tube V206. Resistors R215 andR221 shunt their respective trans-formers, to broaden transformer fre-quency response. Plate and screengrid voltages are supplied from the+125-volt dc distribution bus (par.41e) through decoupling filter R216,

C221 (V205), and R222, C225 (V206).Isolating resistors R247 and R248 con-nect screen grid voltage to their re-spective stages.

(2) As the input signal strength increases,sixth IF amplifier V206 begins to clipthe negative signal peaks because ofits high cathode bias. This clippingof the negative peaks causes V206 tooperate as an infinite impedance de-tector. As the input signal level con-tinues to increase, V205 begins nega-tive peak clipping (detection) and tubeV206 begins limiting due to saturationon the positive signal peaks. TubeV205 will begin positive peak clippingor limiting with a further signal in-crease, and when the input to the re-ceiver is approximately 25 millivolts,IF amplifier V204 (c above) beginslimiting. However, because tube V204has normal bias it does not serve as adetector.

(3) Third detector pickoff diode CR203operates as a conventional second de-tector, rectifying the 60-mc RF pulsesfrom transformer T207 to obtain thevideo pulses. Capacitor C228 addssufficient capacity; this enables T207to tune to approximately 57 mc. Thefirst and second detector pickoff di-odes CR201 and CR202 aid the infiniteimpedance detector action of the fifthand sixth IF stages respectively, bycoupling the positive pulses from thegrid circuits. Capacitors C217, C222,and C227 filter the RF componentfrom the outputs of CR201, CR202,and CR203, respectively. Resistors218, R219, and R223 isolate each ofthe diodes from the common output.Inductors L208 and L210, with capaci-tors C218, C219, and C226, form asmall delay line (or phase shift net-work). This line is terminated ateach end by resistors R217 and R224to match the line impedance correctly.The small amount of phase shift pro-vided by the line compensates for theslight phase shift through each stage.

(4) Successive detection (B, fig. 14) re-sults by addition of the individual di-

26 AGO 10004A

27

Figure 14.

Figure 15.

ode output curves to form an outputto tube V207A, which increases at alinear rate with a logarithmic increasein receiver signal input. The videopulse output (positive pulses) at theDET test point is the sum of the in-dividual outputs of diodes CR201,CR202, and CR203 and is very nearlylinear until the receiver reaches satu-ration. Bias levels of the fourth, fifth,and sixth IF stages are set to causesaturation limiting at one of thesestages when the pickoff diode follow-ing it has reached maximum output.This action prevents overloading apickoff diode, causing nonlinearity inthe resultant sum output. The linearoutput characteristic of the IF, stagesis necessary so that amplitude differ-ences between interrogation pulsesand unwanted pulses may be comparedin the suppressor (f below). There-fore, a desired interrogation pulsepair (normally having equal ampli-tudes) may be selected by the sup-pressor, and all other pulses or pulsepairs are rejected.

e. First Video Amplifier and Cathode Fol-lower (fig. 15). Video pulses are coupled throughinductor L212 to the grid of first video amplifierV207A. Inductor L212 blocks any stray RFfrom the video amplifier input. Degenerativecathode feedback developed across unbypassedresistor R228 helps to maintain good pulse re-

sponse of the amplifier. Resistor R227 is theamplifier plate load, and plate voltage is re-ceived from the +125-volt dc distribution bus(par. 41e). Pulse output from amplifier V207Ais coupled directly to the grid of cathode fol-lower V207B. A large cathode bias resistor,R229, provides the correct bias for V208B, com-pensating for the high positive grid voltagecaused by direct coupling, The plate of V207Bis directly connected to the +125-volt dc bus.The video pulse output of V207B is coupled fromthe cathode through capacitor C231 to thesuppressor.

f. Suppressor (fig. 16). First video cathodefollower V207B applies negative pulses devel-oped across resistor R229 to capacitor C231.Because of the rapid rise and decay time ofthese pulses (0.2 to 0.4 usec), C231 appears asa short circuit during the pulse rise and decaytime, Another important factor in the theoryof operation of the suppressor circuit is theresistance capacitance (rc) time constant ofthe discharge and charge circuits. These timeconstants directly affect the instantaneous volt-ages at various circuit points in the suppressor,and have a direct relationship to the signalpulses applied to the suppressor.

(1) Under static or no-signal conditions,voltages are established at specific cir-cuit points by the +125-volt dc dis-tribution bus (par. 41e), the -150-volt dc distribution bus (par. 42), andthe +3 volts dc obtained across resis-tor R240 in series with part of the

28

IF suppressor subchassis filamentstring (par. 43). Diodes CR204through CR207 operate as electronicswitches in the suppressor circuit; di-odes CR205, CR206, and CR207 areclosed whenever their anodes are aminimum of 0.5 volts positive withrespect to their cathodes, while diodeCR204 requires a minimum of approxi-mately 0.25 volts to close. DiodesCR204, CR206, and CR207 are closedor conducting under static conditions,and diode CR205 is open.

Note. Voltages in the following paragraphsare as measured between the point noted andchassis ground, unless otherwise specified.

(2) Under static conditions, capacitorC231 has a net potential across it ofapproximately 82 volts, and is chargedto this value. The first interrogationpulse fed to tube V207B decreases thecathode voltage. This negative change,coupled through capacitor C231, drivesthe SUPPR test point negative. Whenthe test point reaches -0.5 volt, diodeCR205 closes and capacitor C231 dis-charges to the amplitude of the inputpulse. Throughout the duration of thepulse the SUPPR test point is main-tained at -0.5 volt by CR205. If thecathode voltage of tube V207B is re-duced to +61 volts and the SUPPRtest point voltage is maintained at-0.5 volt, the net potential acrosscapacitor C231 will be 61.5 volts (adifference of 24.5 volts from staticnet potential). The discharge pathfor C231 through diode CR205 andresistor R229 gives the circuit a timeconstant of approximately 0.6 usec.This time constant, nearly the pulsewidth of the normal interrogationpulse, permits capacitor C231 to dis-charge the full amplitude of the inputpulse (24 volts).

(3) During the negative excursion of theinput pulse, the SUPPR test point isonly permitted to drop to the -0.5-volt level by diode CR205. DiodeCR204 will be closed during this time,and the voltage at the grid of tubeV208A will drop to approximately

AGO 10004A

-0.25 volts, thus opening diodeCR207. A negative pulse (limited toa little under 4 volts in amplitude)is applied to the grid of tube V208A.

(4) When the input pulse is no longer pres-ent at the cathode of V207B, capacitorC231 begins to charge through resis-tors R236 and R230 and tube V207B.The voltage at the SUPPR test pointbecomes approximately 21 volts (thepulse amplitude less the static 3-voltpotential at the test point). This posi-tive voltage will open diodes CR204,CR205, and CR206. The absence of anegative pulse will allow diode CR207to close, causing the grid of V208A toreturn to the static reference level of+3.5 volts. Thus, signal input to tubeV208A will resemble the first inter-rogation pulse except for a reductionin amplitude.

(5) If a second pulse does not closely fol-low the first input pulse (15 usec orless), the charge current of capacitorC231 will cause the SUPPR test pointvoltage to decay to the static level.The initial part of this voltage decayis quite linear, and this is the principalportion used for pulse suppression (2usec after the first pulse is received).After approximately 15 usec, the testpoint voltage reduces to the staticlevel of +3 volts, and diodes CR204and CR206 will close, returning thesuppressor circuit to its static condi-tion.

(6) If a second pulse is received during the15-usec decay time, it must have anamplitude greater than the voltagepresent on the SUPPR test point to becoupled through CR203 to the gridof V208A. The decay voltage is highenough for the first 2 usec to blockany pulse that may occur. After 2usec, a second pulse must have anamplitude within 10 db (3.16 volts)of the first pulse, or it will not passon to the grid of V208A. The interro-gation pulses are spaced 3, 5, or 8 usec,and are of a constant amplitude; there-fore any proper interrogation pulsepair will be passed by the suppressor.

29

Figure 16. Suppressor, simplified schematic diagram.

Figure 17. Second video amplifier and cathode follower, partial schematic diagram.

g. Second Video Amplifier and Cathode Fol-lower (fig. 17). Negative video pulses fromthe suppressor are applied to the grid of secondvideo amplifier V208A. Cathode self-bias forV208A is provided by resistor R233, and platevoltage is supplied from the +125-volt dc bus(par. 41e) through plate load resistor R232.Positive pulses from V208A are coupled throughcapacitor C251 to the grid of cathode follower

V208B. Resistor R241 provides a grid returnfor V208B, and the plate is directly connectedto the +125-volt dc distribution bus (par. 41e).Two cathode resistors (R234 and R235) supplyoperating bias and two output voltage and im-pedance levels. The two video outputs at pinsNo. 3 and 9 of receptacle J203 are connected tothe video amplifier card and front panel RCVROUT jack J104, respectively.

30 AGO 10004A

28. Video Amplifier Card(fig. 18)

a. General. The input interrogation pulses tothe video amplifier card are positive in polarityand 0.7 usec in width. Spike suppressor V301eliminates all received pulses having a widthof 0.3 usec or less; these pulses are usuallynoise pulses. The output of V301 consists ofnegative pulses approximately 0.4 usec inwidth. Inverter tube V302A amplifies and in-verts the negative pulses from tube V301 andapplies them to blanked cathode follower V302B.Positive 0.4 usec pulses from V302B are appliedto decoders V351, V352, and V353 on the de-coder card for interrogation mode determina-tion. After a pulse pair is passed to the de-coders, a positive main gate pulse (approxi-mately 120 usec ) is received by blanking cathodefollower V303A. The blanking cathode followerapplies the positive main gate to SUPPR jackJ106 and blanking amplifier V303B. Blankingamplifier V303B amplifies and inverts this gatepulse, and applies it to blanked cathode followerV302B. These negative pulses cut off tubeV302B, preventing spurious video pulses frompassing to the decoder card. Main gate pulsesare also coupled from blanking cathode followerV303A to A.O.C. amplifier V304 where theyare amplified and applied to the A.O.C. rectifier.The A.O.C. rectifier, consisting of CR301through CR303, provides negative bias for IFamplifiers V202, V203, and V204. The A.O.C.

circuit prevents exceeding the permissibletransmitter duty cycle when many interroga-tions are received.

b. Spike Suppressor and Inverter (fig. 19).The input positive video pulses at pin No. 7 ofcard connector P301 are coupled through capaci-tor C301 and developed across resistor R301.These pulses are applied simultaneously to thesuppressor grid of spike suppressor V301 and0.3-usec delay line DL301. The output ofDL301 occurring 0.3 usec after the input, isapplied across resistor R302 to the control gridof tube V301. Both grids are biased to cutoffby voltages from the -150-volt dc distributionbus (par. 42) input at pin No. 10 of card con-nector P301. Tube V301 is able to conduct onlywhen suppressor grid and control grid are bothdriven positive by pulses. The input pulses tothe spike suppressor are of a fixed amplitude,and, because of the 0.3-usec delay of the pulsesapplied to the control grid, pulses of 0.3 usecor less duration will not overlap and allowV301 to conduct. Plate voltage for V301 is sup-plied from the +125-volt dc distribution bus(par. 41e) through plate-load resistor R303.Capacitor C302 couples the negative videopulses from V301 and applies them across gridresistor R304 of inverter V302A. InverterV302A is unbiased to permit a full negativepulse signal swing without clipping. Plate volt-age for tube V302A is supplied from the +125-volt dc distribution bus (par. 41e) through

AGO 10004A

Figure 18. Video amplifier cord, block diagram.

31

Figure 19. Spike suppressor and inverter, partial schematic diagram.

Figure 20. Blanking cathode follower and blanking amplifier, schematic diagram.

plate-load resistor R305, and video output iscoupled through capacitor C303 to blankedcathode follower V302B. Interrogation pulsesare now only 0.4-usec wide and pulse separationis increased by 0.3 usec, which remains withindecoder tolerances.

c. Blanking Cathode Follower and BlankingAmplifier (fig. 20). A positive main gate pulse,approximately 120 usec in width, is applied topin No. 9 of card connector P301 after a cor-rect interrogation pulse pair has been received.This main gate pulse is coupled through capaci-tor C304 across grid resistor R308 to the gridof blanking cathode follower V303A. TubeV303A is negatively biased by the -150-voltdc distribution bus (par. 42) through resistorR316 to allow full swing of the positive pulse

32

without clipping. The low impedance outputsignal developed across cathode resistor R309is coupled directly to blanking amplifier V303Band front-panel SUPPR jack J106. Anotheroutput is coupled through capacitor C306 to thegrid of A.O.C. amplifier V304 (e below). TubeV303B amplifies the main gate pulse and appliesit as a negative gate through capacitor C303 tothe grid of blanked cathode follower V302B(par. 28d). Plate voltage for tube V303B issupplied from the +125-volt dc distribution bus(par. 41e) through plate-load resistor R305.Self-bias is obtained from cathode resistor R310.

d. Blanked Cathode Follower (fig. 21). Twoinputs are coupled through capacitor C303 toblanked cathode follower V302B grid: a posi-tive video pulse pair from inverter V302A, and

AGO 10004A

Figure 21. Blanked cathode follower, partial schematic diagram.

a negative main gate pulse from blanking am-plifier V303B. Tube V303B is operated veryclose to cutoff because of cathode resistor R306and the fixed bias obtained from voltage dividernetwork R307 and R313 connected between the-150-volt distribution bus (par. 42) andground. The plate is directly connected to the+125-volt dc distribution bus (par. 41e). Thefirst interrogation pulse pair passes throughV303B, is decoded in the decoder card (par.29), and triggers the main gate multivibrator.The output of the main gate multivibrator isused to cut off tube V303B, preventing interro-gations from triggering the transponder forapproximately 120 usec after the pulse pairis passed.

e. A.O.C. Amplifier and Rectifier (fig. 22).The two sections of A.O.C. amplifier V304 areconnected in parallel The positive main gatepulse is coupled through capacitor C306 andgrid-limiting resistor R311 to both grids. Biasfrom the -150-volt dc distribution bus (par.42) is applied to both grids by voltage-dividerresistors R314 and R315, to permit large sig-nal swings without clipping. Negative outputpulses developed across plate-load resistorR312 of V304 are coupled through capacitorC305 to a voltage-doubler rectifier consistingof diodes CR301 and CR302. Resistors R317and R318 provide the load for the voltage-doubler rectifier. The voltage across variableresistor R318 charges capacitor C307 duringeach main gate. Zener diode CR303 has a break-down (Zener) voltage from 9 to 12 volts. Whenthe average charge potential across capacitorC307, governed by the main gate pulse repeti-

AGO 10004A

tion rate and resistor R318 setting, reachesthis voltage, diode CR303 conducts. When diodeCR303 conducts, a negative voltage is appliedto IF amplifiers V202, V203, and V204 (par.27b and c), reducing the receiver sensitivity.When the frequency of the main gate pulse in-creases, capacitor C307 has less time to dis-charge between main gate pulses; this in-creases the average voltage across capacitorC307. The main gate pulse amplitude and dura-tion are constant; therefore the only two factorsaffecting capacitor C307 voltage are the repeti-tion rate and the adjustment of resistor R318.

29. Decoder Card(fig. 23)

a. General. Interrogation pulse pairs areapplied directly and through delay line DL351to three decoders V351, V352, V353. Delay lineDL351 has three delayed outputs correspondingin time to the pulse separations of the threeinterrogation modes used in the Mark X IFFSystem. This delay enables tube V353 to passonly mode 1 interrogations; tube V352, mode2; and tube V351, mode 3. The decoder cardhas several outputs; three direct outputs, allow-ing each decoder to trigger its mode gate multi-vibrator; a direct connected all-mode outputthat triggers the main gate multivibrator; anall-mode output controlled by switching diodeCR354 that triggers mode 1 gate multivibratorand the ring around gate multivibrator forNORMAL-EMER or NORMAL-l/P repliesand modes 1 and 3 outputs controlled by switch-ing diodes CR355 and CR356, to trigger thering around gate multivibrator for MOD-EMER, MOD-I/P, or CIVIL-EMER replies.

33

Figure 22. A.O.C. amplifier and rectifier, partial schematic diagram.

All of the above decoder outputs are singlenegative pulses 0.4 usec in width.

b. Modes 1, 2, and 3 Decoders (fig. 24). Thedecoders consist of three identical coincidenceamplifier stages. The interrogation mode is de-termined by comparing the second pulse of anincoming pulse pair, at pin 3 of receptacleJ351 and card connector P351, with the firstpulse delayed 3, 5, or 8 usec. Each of the threetubes (V351, V352, and V353) has its controlgrids and suppressor grids biased beyond cutoffby -150-volt dc distribution bus (par. 42),through dropping resistor R363. Plate voltagefor the three tubes is supplied from the +125-volt dc distribution bus (par. 41e) throughplate load resistors R352, R355, and R358. Thesmall difference in plate load resistances ad-justs the amplification of the decoders to com-pensate for slight signal losses in the delayline. Ground return for the grids is providedby resistors R353, R356, and R359; resistorR351 and capacitor C351 in series match thetermination impedance of delay line DL351.A received interrogation pulse pair, coupledthrough capacitor C357, is fed simultaneouslyto the suppressor grids of all three decoders,and to delay line DL351 input. Pin 17 of cardconnector P351 applies the first pulse to thecontrol grid of tube V353 3 usec after it ap-peared on the suppressor grids. Pin 8 of cardconnector P351 applies the first pulse to thecontrol grid of tube V352 5 usec after it ap-peared on the suppressor grids, and pin 2 ofcard connector P351 applies the first pulse to

34

the control grid of tube V351 8 usec after itappeared on the suppressor grids. A mode 1interrogation consists of two pulses with aseparation of 3 usec; under these conditions,the only tube that will amplify is V353 (Mode1 decoder) because the 3-usec delay of delayline DL351 has applied the first pulse to thecontrol grid at the same time the second pulseis applied to the suppressor grids. The modes2 and 3 decoders operate in the same mannerto identify the modes 2 and 3 interrogationsspaced 5 and 8 usec, respectively. When a de-coder operates, the single pulse appearingacross its plate load resistor is coupled to thedecoder output distribution network (c below).Therefore, each decoder can conduct and pro-duce a single output pulse if the second pulseon the suppressor grid coincides with the firstpulse after it has been delayed. CapacitorsC354, C353, and C352 couple modes 1, 2, and3 trigger pulses, respectively, to the output dis-tribution network.

c. Recoder Output Distribution (fig. 25). Theoutputs from the mode decoders consist of 0.4usec negative pulses occurring at the same timethe second interrogation pulse of a pulse pairwas received at the decoder card. The mode 1trigger pulse coupled through capacitor C354across resistor R361, will trigger mode 1 gatemultivibrator V401 in the gate generator card(par. 30). Diode CR358 prevents this negativepulse from feeding back into other circuitry.A mode 2 trigger pulse coupled through C353across resistor R357 will trigger mode 2 gate

AGO 10004A

Figure 23.

35

Figure 24.

multivibrator, and a mode 3 trigger pulsecoupled through C351 across R354 will triggermode 3 gate multivibrator V403. Diodes CR351,CR352, and CR353 couple their respective modeoutputs to main gate multivibrator V404. Eachof these diodes prevent the other two modetrigger pulses from entering its output circuit.Resistor R360 terminates the main gate multi-vibrator common trigger pulse line. DiodesCR354, CR355, and CR356 perform switchingfunctions, and are cut off by a negative biasfrom the -150-volt dc distribution bus (par.42). Diode CR354 sets up ring around gate

36

multivibrator V503 with decoder output pulsesfor EMER and I/P categories of NORMALfunction, and diodes CR355 and CR356 providering around decoder pulses for MOD-EMER,MOD-I/P or CIVIL-I/P categories.

(1) Diode CR354 receives its cutoff biasfrom voltage divider resistors R364and R365 bypassed by C356 andthrough R362. This bias is removedwhenever emergency-normal relay K4(par. 43) energizes connecting pin 16of card connector P351 to ground. Re-lay K4 will energize if the control unit

AGO 10004A

Figure 25.

37

(2)

(3)

function control is set to NORMALand either I/P or EMER operation isused. Under these conditions, an inter-rogation in any mode will trigger ringaround gate multivibrator V503 in theblocking oscillator and ring aroundcard (par. 31). The all-mode pulse iscoupled through CR354 and C358 anddeveloped across resistor R372. DiodeCR357 passes the trigger pulse to pin13 of card connector P351 but preventsmultivibrator V503 output from feed-ing back through the decoder outputdistribution circuits. Capacitor C355couples all-mode trigger pulses acrossresistor R373 and the output of CR358triggers mode 1 gate multivibratorV401 (par. 30b).The cutoff bias for diodes CR355 andCR356 is supplied by voltage dividerresistors R367 and R369, bypassed bycapacitor C360. Pin 6 of card con-nector P351 is grounded by emergencymodified relay K3 (par. 46g) when-ever the control unit master switch isset to EMER or; whenever the controlunit is set to I/P and the function con-trol is set to MOD. Resistor R370 isthe load resistor for CR356 and mode3 trigger pulses; and R368 the load forCR355 and the mode 1 trigger pulses.Capacitors C359 and C361 couple theModes 1 and 3 pulses across load re-sistor R371. These pulses are appliedto ring around gate multivibratorV503 in the blocking oscillator andring around card (par. 31c).The decoder output distribution cir-cuit supplies the necessary triggerpulses to the ring around gate multi-vibrator for the repetitive character-istics of I/P and EMER replies. Mode2 interrogations are answered withrepeated replies in NORMAL functiononly.

30. Gate Generator Card(fig. 26)

a. General. Modes 1, 2, and 3 gate multivibra-tors V401, V402, and V403 have identical cir-cuits that produce three independent 120-usecmode gate pulses according to the interrogation

38

Figure 26. Gate generator card, block diagram.

mode. Each of the three multivibrators, whentriggered by a 0.4-usec negative pulse from theappropriate mode decoder, supplies its gate tothe appropriate mode reply selector. Mode 1gate multivibrator V401 is also triggered inEMER and I/P (except CIVIL) functions by acombined mode pulse. Each mode gate multi-vibrator output is applied to its respective modereply selector in the mode reply selector card(par. 35) allowing the selector to assembly thedesired reply train. Main gate multivibratorV404 is triggered by a 0.4-usec negative pulsefrom any of the mode decoders, and suppliesthe following output gates:

(1)

(2)

(3)

A negative gate applied through themain gate amplifier to the video ampli-fier card (par. 28), for video blankingand A.O.C.A negative pulse to the ringing oscil-lator and coincidence card (par. 36)that allows ringing oscillator V551 tooperate.A positive gate to the blocking oscil-lator and ring around card (par. 31)that triggers and allows encoder block-ing oscillator V501 to operate.

AGO 10004A

Figure 27.

39

Figure 28.

b. Mode 1 Gate Multivibrator (fig. 27). Gridpin 2 of tube V401 is positive biased by resistorR401 connected to the +125-volt dc distributionbus (par. 41e) to cause plate current saturation.Identical plate load resistors R403 and R404 areused for both sections of tube V401, and grid pin7 is negative biased with voltage divider re-sistors R405 and R406 connected from the-150-volt dc distribution bus (par. 42) toground. Resistor R402 is a common cathode-biasing resistor to control operating bias whentube V401 oscillates. Capacitors C402 and C403are feedback coupling capacitors. When a nega-tive decoder pulse is coupled through C401 togrid pin 2, pin 1 plate current is driven to cut-off; this drives grid pin 7 positive through C403.Grid pin 7 going positive increases pin 8 platecurrent and the negative going plate voltage iscoupled back to hold grid pin 2 at cutoff. Thedecoder input pulse has collapsed by this timeand pin 1 plate current is cutoff and pin 8 platecurrent has reached saturation. The length oftime this condition exists (determined by thecharge and discharge rates of capacitors C402and C403) sets the width of the gate pulse.When this static condition is reached, capacitorsC402 and C403 reverse and drive the tube sec-

tions back to the static starting voltages presentbefore the decoder trigger pulse arrived. Apositive mode gate pulse is coupled from platepin 1 directly to the mode 1 reply selector tubeV451 (par. 35b) through pin 2 of card connectorP401.

c. Modes 2 and 3 Gate Multivibrators (fig.27). The circuits for modes 2 and 3 gate multi-vibrators are similar to mode 1 gate multi-vibrator (b above). Pin 7 of V402 and pin 2of V403 grids are positive biased by resistorsR407 and R413 connected to the +125-volt dcdistribution bus (par. 41e), causing plate cur-rent saturation of this section. The other sec-tion of each of these multivibrators is cutoffby negative bias from the -150-volt distribu-tion bus (par. 42) through two separate voltagedividers. Resistors R412 and R411 apply thecutoff bias to the grid pin 2 of V402, and re-sistors R418 and R417 apply cutoff bias to thegrid pin 7 of V403. Resistors R408 and R414are the common cathode resistors for the twomultivibrators. Identical plate load resistors arealso used; resistors R409 and R410 for V402,and R415 and R416 for V403. The cross-con-nected feedback between the two triode sectionsof each multivibrator is provided by capacitors

40

C406, C405, C408, and C409. The trigger inputto V402 from the mode 2 decoder is connectedto pin 4 of card connector P401 and is coupledto grid pin 7 through capacitor C404. Thetrigger input from mode 3 decoder connected topin 9 of card connector P401 is coupled throughcapacitor C407 to the grid pin 2 of V403. Theoutput gates from these decoders, connected topins 6 and 8 of card connector P401, are appliedto their respective reply selector.

d. Main Gate Multivibrator (fig. 28). Al-though main gate multivibrator V404 operationis similar to multivibrators V401, V402, andV403, its circuit is altered to better accommo-date its multiple outputs. The pin 2 grid sectionis biased to plate saturation by the applicationof a high negative cathode bias through resistorR426 from the -150-volt dc distribution bus(par. 42). The grid is returned to groundthrough resistor R419. Plate pin 1 has R420 asplate load resistor and plate pin 8, R421; bothobtain plate voltage from the +125-volt dc dis-tribution bus (par. 41e). Grid pin 7 is biasedto cutoff by voltage divider resistors R423 and

R424 from the -150-volt dc distribution bus(par. 42). Capacitors C411 and C412 are feed-back coupling capacitors, and cathode resistorR422 at pin 5 provides additional operatingbias. A negative trigger pulse from the decoder,coupled through C410, drives pin 2 grid nega-tive causing pin 1 plate voltage to increase. Thepositive voltage change is coupled by capacitorC411 to grid pin 7, driving pin 8 plate towardsaturation. This increased plate current causescathode pin 5 to become more positive. Thepositive increase at pin 5 is coupled throughcapacitor C412 to cathode pin 4, driving platepin 1 to cutoff. Circuit time constants hold tubesaturation. for approximately 120 usec before itcan return to the static condition. Positive maingate pulses are taken from cathode pin 4 tooperate trigger amplifier V501A in the blockingoscillator and ring around card (par. 31). Nega-tive pulses are taken from plate pin 8 to operateringing oscillator driver V551A in the ringingoscillator and coincidence card (par. 36), andto be amplified by main gate amplifier V454A inthe mode reply selector (par. 35d) for videoblanking and A.O.C.

Section IV. ENCODER-TRANSMITTER THEORY

31. Blocking Oscillator and Ring Around Card(fig. 29)

a. General. The blocking oscillator and ringaround card supplies one or more excitationpulses to delay line DL601, from which all codedreply trains are formed. Isolating diode CR501couples and differentiates the main gate pulsefrom main gate multivibrator V404 to the inputof trigger amplifier V501A. The output of tubeV501A triggers encoder blocking oscillatorV501B, which supplies a 1-usec positive pulse todelay line DL601. During EMER and I/P oper-ations, the reply train must be repeated al-though only one interrogation pulse pair wasreceived. To initiate this repeat, an all-modetrigger pulse is supplied to ring around gatemultivibrator V503 which generates a gatepulse of either 37, 57, or 87 usec in width. The37-usec ring around gate pulse is used in MOD-I/P (par. 46f) only, the 57-usec gate in NOR-MAL-I/P and NORMAL-EMER (par. 46c andd), and the 87-usec in the MOD-EMER andCIVIL-EMER (par. 46g and j) conditions.These ring around gate pulses allow gated

AGO 10004A

amplifier V502 to amplify ring around triggerpulses obtained from the ring around bus in themode 1 reply code switching card (par. 32).The output pulses of tube V502 are applied totrigger amplifier V501A to start encoder block-ing oscillator V501B. Only three ring aroundpulses (from the mode 1 bus) occur during thering around gate. Actually, the first reply trainis triggered by the original interrogation andonly three more reply trains are needed to com-plete MOD-EMER operation.

b. Trigger Amplifier and Encoder BlockingOscillator (fig. 30). Trigger amplifier V501Ais biased to cutoff by voltage divider resistorsR502 and R503, connected to the -150-volt dcdistribution bus (par. 42). Its plate is con-nected in parallel with the plate of encoderblocking oscillator tube V501B to a commonplate load consisting of the primary of trans-former T501 paralleled by resistor R522. Platevoltage is supplied by the +125-volt dc distribu-tion bus (par. 41e). The positive pulses frommain gate multivibrator V404 (par. 30d) at pin

41

Figure 29.

3 of card connector P501 are coupled throughisolating diode CR501 to resistor R501. DiodeCR501 prevents trigger amplifier input pulsesfrom returning to main gate multivibratorV404, and assists coupling capacitor in differ-entiating the main gate pulse. Isolating diodeCR501 allows coupling capacitor C501 to chargerapidly to the positive main gate pulse ampli-tude. Trigger pulses for repetitive reply con-struction during EMER and I/P operations areobtained from gated amplifier V502 throughtransformer T502 and coupling capacitor C502.Diode CR502 clips the negative pulse peaks fromthe output of transformer T502 secondary.Fixed bias for encoder blocking oscillator V501Bis supplied by voltage divider resistors R505 andR506 connected to the -150-volt dc distributionbus (par. 42), and self-bias is provided by cath-ode resistor R521. Capacitor C503 eliminatesdegeneration caused by cathode resistor R521.A positive trigger pulse, fed to tube V501A in-put, causes plate current to increase through theprimary of transformer T501. A positive volt-age induced in the secondary is applied to thegrid of tube V501B. The encoder blocking oscil-lator grid is quickly driven positive and drawscurrent, charging capacitor C513. The rate andamount of charge of capacitor C513 are deter-mined by the setting of resistor R523. After thetrigger pulse reaches maximum amplitude, therate of plate current change begins to diminish,and the secondary voltage of transformer T501

42

reduces. When the charge voltage of capacitorC513 equals the secondary voltage of trans-former T501, they cancel because of oppositepolarities. The static fixed bias then cuts offtube V501B and the magnetic field of trans-former T501 begins to callapse, reversing thesecondary voltage polarity. This reversal drivestube V501B further into the cutoff region,sharpening the trailing edge of the generatedpulse. Ringing oscillations are eliminated inthe encoder blocking oscillator by the slow dis-charge of capacitor C513, keeping the grid be-low cutoff. Desirable trigger pulses throughtrigger amplifier V501A have sufficient ampli-tude to overcome this additional bias when re-quired. The encoder blocking oscillator output,taken from the cathode of tube V501B, is a pulseof approximately 1 usec in width as determinedby the setting of resistor R523. This pulse isapplied to delay line DL601.

c. Ring Around Gate Multivibrator (fig. 31).Multivibrator tube V503 is a conventional mono-stable multivibrator capable of providing anoutput gate with one of three different pulsewidths. Resistors R515 and R516 are plateloads, and capacitors C510 and C511 are feed-back coupling capacitors. A voltage divider con-sisting of resistors R517 and R518, in serieswith R515 between the +125-volt and -150-volt dc distribution buses, supplies negative biasto grid pin 7. Grid pin 2 is positive biased tosaturate plate (pin 1) current. The value of this

AGO 10004A

Figure 30.

Figure 31.

43

Figure 32.

44

positive grid voltage is determined by resistorR524 and whether the +125-volts dc is suppliedthrough resistor R511, R512; or R513. Capaci-tors C506, C507, and C508 prevent pulses fromentering the +125-volt dc distribution bus (par.41e). Common cathode resistor R514 sets theoverall operating bias to the optimum condition.A negative trigger pulse from the decoder card(par. 29) is coupled through capacitor C509 togrid pin 2 to cutoff plate (pin 1) current. Theincreasing plate voltage at pin 1 is coupledthrough capacitor C511 to grid pin 7, saturatingpin. 8 plate current. The decreasing voltage atthe plate, pin 8, is coupled through capacitorC510 to drive the grid, pin 2, into cutoff. Duringthis cutoff period, capacitor C510 must dis-charge through one of the selected resistors(R511, R512, or R513) before grid pin 2 re-turns to the high positive static bias condition.The length of time grid pin 2 is cut off deter-mines the ring around gate multivibrator out-put pulse width. The positive gate pulses arecoupled through capacitor C504 to gated ampli-fier V502. Resistor R511 provides 37 usecpulses; R512, 57 usec pulses; and R513, 87 usecpulses.

d. Gated Amplifier (fig. 32). Gated amplifierV502 requires two positive pulse inputs beforeplate current will flow, developing an outputacross the secondary of transformer T502. Sup-pressor grid cutoff bias is supplied by voltagedivider resistors R509, R510, and control grid

cutoff bias is -150-volts dc unless modified-emergency relay K3 is energized. EnergizingK3 grounds pin 10 of card connector P501 anddrops the control grid bias to approximately-25 volts through voltage divider resistorsR507 and R508. Capacitor C512 bypasses sig-nals from the modified-emergency relay circuitwhen K3 is not energized. If relay K3 is ener-gized the positive 37-, 57-, or 87-usec ringaround gate multivibrator pulses coupledthrough capacitor C504 bring the control gridout of cutoff. During the time of this gate,positive pulses applied to the suppressor gridwill appear in the plate circuit. These positivepulses are obtained from the ring around busin the mode 1 reply code switching card (par.32) through pin 8 of card connector P501 andcoupling capacitor C505. Positive trigger pulsestaken from the secondary of transformer T502are coupled through capacitor C502 to triggeramplifier V501A. Base shaper CR502 clips thenegative peak swing of the ouput pulses.

32. Mode 1 Reply Code Switching(fig. 33)

a. General. Mode 1 I/P and EMER replies(consisting of repeated replies) are described inparagraph 46. The formation of single repliesor reply trains for each category are listed be-low. In MOD or CIVIL, the reply train consistsof the first and last framing pulses with up tosix information pulses selected by the MODE 1

code control. The MODE 1 code control consistsof two concentric selector switches S901A andS901B. NORMAL replies consist of individualpulses only.

b. Mode 1 Normal Replies. Mode 1 NORMALreplies, a single pulse (A, fig. 5), are providedby the direct ground from pin M of receptacleJ901, pin 15 of J112, and pin 26 of card con-nector P621. This ground removes the +60-voltdc cutoff bias applied to diode CR621 throughresistors R621 and R622. The O-usec pulse fromterminal 1 of delay line DL601 is developedacross resistor R621 and coupled to Mode 1 replyselector V451 bus 1 by capacitor C622. Al-though relay K1 is closed when switch S903 isin the NORMAL position (par. 46b), the 15.05-usec pulse fed to gated amplifier V502 by diodeCR627 and capacitor C634 is not effective be-cause gated amplifier V502 is cut off. Functioncontrol S903 removes the ground connectionfrom MODE 1 control S901, eliminating codecontrol pulse selection.

c. Mode 1 MOD or Mode 1 CIVIL Replies.(1) Framing pulses. MODE 1 code control,

selector switches S901A and B areactivated by the ground supplied totheir number one arm contacts fromfunction control S903 (set to MODor CIVIL). This ground, through pinA of receptacle J901 and pin 10 ofcard connector P621, closes switchingdiode CR629 and applies the 20.3-usec pulse from terminal 15 of DL601to bus 1 through capacitor C638 asthe last framing pulse. The first fram-ing pulse is supplied by the closing ofswitching diode CR621 through theground from pin M of receptacle J901(as in b above), selecting the 0-usecpulse to bus 1. The two framing pulseswill always be present for modifiedor civil replies regardless of MODE1 code control S901 position, and arethe only pulses present in a reply whenS901 is in the 00 position.

(2) Group A (tens) pulses. The group A(tens) pulses are selected throughseven positions of switch S901A. The2.9-usec delayed pulse (A1 pulse, fig.5) is produced when contact 2 or 4of switch S901A rear supplies theground connection through pin C of

J901 and pin 24 of card connectorP621 to close switching diode CR622.Contact 2 or 4 is closed in the 1, 3, 5,and 7 dial number positions. Pulsesare developed across resistor R623 andcoupled to bus 1 by capacitor C624.Contacts 3, 8, and 12 of S901A rearsupply a ground through pin D ofJ901 and pin 22 of J621, at dial num-bers 2, 3, and 6 closing switch diodeCR623 to produce the 5.8-usec pulse(A2 pulse, fig. 5) which is coupledthrough capacitor C626. The remain-ing group A pulse (A4 pulse, fig. 5)is an 8.7-usec delayed pulse producedby the ground from contact 5 on switchS901A front through pin C of J901and pin 20 of P621. This ground ispresent in the 4, 5, 6, and 7 dial num-ber positions. This ground closesswitching diode CR624 and developsthe pulse across resistor R627 andthrough capacitor C628 to bus 1.

(3) Group B (units) pulses. The group B(units) switching section of MODE 1code control is limited to three posi-tions as the available assigned codenumbers (par. 21a) are limited. Con-tacts 2 and 4 of switch S901B rearapply the ground which closes switch-ing diode CR625 in the 1 and 3 dialnumber positions only. The 11.6-usecpulses (B1) are developed across re-sistor R629 and coupled to bus 1through capacitor C630. Contact 3of switch S901B rear closes switchingdiode CR628, and although contacts8 and 12 would do the same, the switchcannot rotate far enough to accom-plish this. Thus, the 14.5-usec de-layed pulse (B2 pulse, fig. 5) is usedonly in the dial number 2 position.

33. Mode 2 Reply Code Switching(fig. 34)

a. General. Mode 2 coded reply trains, avail-able only in MOD or CIVIL functions and whenMODE 2 switch S905 is set to ON, are controlledby 12 toggle switches (S101 through S112) onthe receiver-transmitter front panel (fig. 6).

b. MODE 2 NORMAL Replies. Mode 2 NOR-MAL replies consist of two pulses, spaced 15.95

AGO 10004A 45

usec (B, fig. 5). Diode CR651 is permanentlyset up to conduct O-usec pulses from delay lineDL601, developing its output pulse across resis-tor R651 and coupling it to bus 2 through capac-itor C651. With switch S903 on NORMAL, relayK1 is energized. Contacts 6/8 of relay K1 applya ground to resistors R670 and R671, removingthe +60-volt dc bias applied to diode CR661.Diode CR661 then passes the 15.95-usec delayedpulse from delay line DL601, developing an out-put across resistor R670, which is coupledthrough capacitor C671 to bus 2. Only thesetwo pulses can be selected in NORMAL function,because the 12 toggle switches are deactivatedby contact 7 of relay K1.

c. Mode 2 MOD or Mode 2 CIVIL Replies.(1)

(2)

46

Framing pulses. Diode CR651 is per-manently set to conduct O-usec pulsefrom delay line DL601 when MODE 2switch S903 is ON. This pulse outputis developed across resistor R651 andcoupled to bus 2 through capacitorC651. When function control S903 isset to MOD or CIVIL, relay K1 is de-energized, and its contacts 6-7 gronndresistors R676 or R677. This groundremoves the +60-volt dc bias fromdiode CR664, permitting it to conductthe 20.3-usec delayed pulse from delayline DL 601. Output of diode CR664 isdeveloped across resistor R676 andcoupled to bus 2 through capacitorC677.Group A (thousands) pulses. GroupA (thousands) pulses are selected byswitches S102, S104, and S106 (frontpanel numbers 1, 2, and 3). The 2.9-usec pulse (A1 pulse, fig. 5) is pro-duced when switch S102 is closed, clos-ing switching diode CR653, the outputof which is developed across resistorR654 and coupled to the outputthrough capacitor C655. The 5.8-usecpulse (A2, fig. 5) is produced whenswitch S104 is closed, closing switchingdiode CR655. The output of diodeCR655 is developed across resistorR656 and coupled to bus 2 throughcapacitor C657. The 8.7-usec delayedpulse (A4, fig. 5) is produced whenswitch S106 is closed, closing switch-

(3)

(4)

(5)

ing diode CR657. The output of diodeCR657 is developed across resistorR662 and coupled to bus 2 throughcapacitor C663.Group B (hundreds) pulses. Group B(hundreds) pulses are selected byswitches S107, S109, and S111 (frontpanel numbers 4, 5, and 6). The 11.6-usec delayed pulse (B, fig. 5) is pro-duced when switch S107 is closed, clos-ing switching diode CR658. The out-put of diode CR658 is developed acrossresistor R664 and coupled to bus 2through capacitor C665. The 14.5 -usecdelayed pulse (B2, fig, 5) is producedwhen switch S109 is closed, closingswitching diode CR660. The output ofdiode CR660 is developed across re-sistor R668 and coupled to bus 2through capacitor C669. The 17.4-usecdelayed pulse (B4, fig. 5) is producedwhen switch S111 is closed, closingswitching diode CR662. The output ofdiode CR662 is developed across re-sistor R672 and coupled to bus 2through capacitor C673.Group C (tens) pulses. Group Cpulses (tens) are selected by switchesS101, S103, and S105 (front panelnumbers 7, 8, and 9). The 1.45-usecdelayed pulse (C1, fig. 5) is producedwhen switch S101 is closed, closingswitching diode CR652. The output ofdiode CR652 is developed across resis-tor R652 and coupled to bus 2 throughcapacitor C653. The 4.35-usec delayedpulse (C2, fig. 4) is produced whenswitch S103 is closed, closing switch-ing diode CR654. The output of diodeCR654 is developed across resistorR656 and coupled to bus 2 throughcapacitor C657. The 7.25-usec delayedpulse (C4, fig. 5) is produced whenswitch S105 is closed, closing switch-ing diode CR656. The output of diodeCR656 is developed across resistorR660 and coupled to bus 2 throughcapacitor C661.Group D (units) pulses. Group D(units) are selected by switches S108,S110, and S112 (front panel numbers10, 11, and 12). The 13.05-usec delayed

AGO 10004A

pulse (D1, fig. 5) is produced whenswitch S108 is closed, closing switch-ing diode CR659. The output of diodeCR659 is developed across resistorR666 and coupled to bus 2 throughcapacitor C667. The 15.95-usec delayedpulse (D2, fig. 5) is produced whenswitch S110 is closed, closing switchingdiode CR661. The output of diodeCR661 is developed across resistorR670 and coupled to bus 2 throughcapacitor C671. The 18.85-usec delayedpulse (D4, fig. 5) is produced whenswitch S112 is closed, closing switch-ing diode CR663. The output of diodeCR663 is developed across resistorR674 and coupled to bus 2 throughcapacitor C675.

34. Mode 3 Reply Code Switching(fig. 35)

a. General. Only NORMAL, MOD, or CIVILmode 3 replies are discussed below, because I/Pand EMER selections are discussed in para-graph 46. The MODE 3 code control consistsof two concentric selector switches S902A andS902B.

b. Mode 3 NORMAL Replies. Mode 3 NOR-MAL replies consists of a single pulse (C, fig.5) which is passed by switching diode CR681.Diode CR681 is permanently set up to conductthe O-usec pulse, by a ground through pin B ofreceptacle J901. The output of diode CR681 isdeveloped across resistor R681 and coupled tobus 3 through capacitor C682.

c. Mode 3 MOD and Mode 3 CIVIL Replies.(1) Framing pulses. MODE 3 code con-

trol selector switches S902A and B areactivated by grounding both numberone arm contacts. This ground is sup-plied by function control S903, whenset to MOD or CIVIL. This groundis also applied through pin j of re-ceptacle J901, to close switching diodeCR695 which supplies a 20.3-usecdelayed pulse to bus 3, through capac-itor C696. This 20.3-usec delayed pulseis the second framing pulse. The firstframing pulse is supplied by switchingdiode CR681 (b above). The twoframing pulses are fixed parts of themode 3 MOD or mode 3 CIVIL replies,

AGO 10004A

regardless of code control S901 set-tings.

(2) Group A (tens) pulses. G r o u p A

(3)

pulses (tens) are selected throughseven positions of switch S902A.These selections are independent of

settings of switch S902B. The 2.9-usecdelayed pulse (A1, fig. 5) is producedin dial positions 1, 3, 5, and 7 whencontact 2 or 4 of switch S902A rearprovides the ground connection toclose switching diode CR683. Theseoutput pulses are developed across re-sistor R683 and coupled to bus 3through capacitor C684. The 5.8-usecdelayed pulse (A2, fig. 5) is producedwhen contact 3, 8, or 12 of switchS902A rear provides the ground con-nection to close switching diode CR684(in the 2, 3, 6, and 7 dial positions).The output of diode CR684 is developedacross resistor R685 and coupled tobus 3 through capacitor C686. The8.7-usec delayed pulse (A4, fig. 5) isproduced when contact 5 on switchS902A front provides the ground con-nection (in the 4, 5, 6, and 7 dial posi-tions) to close switching diode CR687.The output of diode CR687 is developedacross resistor R687 and coupled tobus 3 through capacitor C688.Group B (units) pulses. Group Bpulses (units) are selected throughseven positions of switch S902B (in-dependent of switch S902A settings).The 11.6-usec delayed pulse (B1, fig.5) is produced when contact 2 or 4of switch S902A rear provides theground connection to close switchingdiode CR688 (in the 1, 3, 5, and 7 dialpositions). Output of diode CR688is developed across resistor R689 andcoupled to bus 3 through capacitorC690. The 14.5-usec delayed pulse(B2, fig. 5) is produced when contact3, 8, or 12 of switch S902B rear pro-vides the ground connection to closeswitching diode CR691 (in the 2, 3,6, and 7 dial positions). Output ofdiode CR691 is developed across re-sistor R691 and coupled to bus 3

47

Figure 36.

48

through capacitor C692. The 17.4-usecdelayed pulse (B4, fig. 5) is producedwhen contact 5 of switch S902B frontprovides the ground connection to closeswitching diode CR692 (in the 4, 5,6, and 7 dial positions). The output ofdiode CR692 is developed across re-sistor R693 and coupled to bus 3through capacitor C694.

35. Mode Reply Selector Card(fig. 36)

a. General. The three mode reply selectors(V451, V452, and V453) are identical stagesand their individual identifications are deter-mined by the characteristics of their inputsignals. Each selector receives a gate pulsefrom its respective mode gate multivibrator(par. 30) and the series of pulses selected bythe reply code switching circuits (pars. 32, 33,and 34). Each mode reply selector tube has acommon bus connection from its correspondingmode reply switching card which carries the

code pulses selected from delay line DL601. Fora given interrogation, only one gate will be ap-plied to a reply selector, as determined by theinterrogation mode. All three mode reply trainsfrom the modes 1, 2, and 3 reply switching cardsare applied to the respective reply selectors.The reply selector that receives a gate willapply its coded reply train to the common replyselector connection. The selected pulses on thecommon connection are applied to base shaperdiode CR451. Diode CR451 removes any posi-tive excursions or irregularities before thepulse train is amplified in reply train ampli-fier V454B and fed to coincidence detector V554(par. 36e). This selected reply train is thebasic group which eventually results in thetransponder transmitted reply. Main gateamplifier V454A amplifies the output of maingate multivibrator V404 (par. 30d) for applica-tion as positive pulses to blanking cathode fol-lower V303A (par. 28c) in the video amplifiercard.

Figure 37.

b. Modes 1, 2, and 3 Reply Selectors (fig. 37).Mode reply selectors V451, V452, and V453operate identically when the MODE 2 andMODE 3 control unit switches are ON. Sup-pressor grid bias is supplied from the -150-voltdc distribution bus (par. 42) through resistorsR451-R452, R455-R456, and R459-R460, andcontrol grid bias is taken from a common busestablished by resistors R454 and R457 throughrespective resistors R453, R458, and R461. Ca-pacitors C453 and C456 prevent stray pickupfrom entering the suppressor grid circuit, andcapacitor C452 bypasses any signals on the con-

trol grid bias bus. Resistor R462 is a commonplate load for all three tubes, and plate voltageis obtained from the +125-volt dc distributionbus (par. 41e). Each mode gate pulse, coupledby capacitor C451, C454, or C455 to the controlgrid, overcomes the fixed bias and allows thereply code pulses applied to the suppressor gridto be amplified by the appropriate mode replyselector. The mode gate pulse switches on thecorrect mode reply selector for approximately120 usec to pass the selected code reply train forthat mode. The common outputs are coupledthrough capacitor C457 to base shaper diode

AGO 10004A 49

Figure 39.

Figure 38.

50

CR451. When mode 2 and mode 3 replies arenot required, the control unit removes theground from pins 5 and 9 of card connectorP451, and tubes V452 and V453 are maintainedat cutoff by -150-volt bias on their controlgrids.

c. Reply Train Amplifier (fig. 38). The neg-ative reply train pulses are coupled throughcapacitor C457 to the cathode of base shaperCR451. The cathode of CR451 is maintainedapproximately 15 volts positive by the voltagedivider consisting of resistors R463 and R464.The negative reply train pulses must first over-come this voltage before diode CR454 can applythem across resistor R465 to the grid of replytrain amplifier V454B. This removes any ir-regularities appearing at the reference level ofthe pulse train. Tube V454B amplifies the pulsesand develops them across plate load resistorR466. The positive pulse reply train from tubeV454B is applied to coincidence detector V554through pin 14 of card connector P451.

d. Main Gate Amplifier (fig. 39). Main gate

amplifier V454A is zero-biased to permit largenegative pulse swings without clipping. Theinput to tube V454A, from main gate multi-vibrator V404 (par. 30d), is coupled throughcapacitor C458 to the grid circuit. ResistorR468 is the grid resistor. The positive maingate output pulses developed across plate loadresistor R467 are applied through pin 12 ofcard connector P451 to blanking cathode fol-lower V303A (par. 28c) in the video ampli-fier card.

36. Ringing Oscillator and Coincidence Card(fig. 40)

a. General. A negative main gate pulse isapplied through driver V551A to excite the ring-ing oscillator V551B. During the approximate120-usec period of this main gate pulse, theringing oscillator produces slightly dampedsine waves with a one-cycle period of 1.45 usec(approximately 690 kc). The sine wave issquared by first and second clippers V552A andV552B and differentiated by tube V553A. Theoutput of differentiator V553A, consisting of a

51

Figure 40.

series of accurately timed (1.45 usec) pulses,is fed to coincidence detector V554 togetherwith the selected reply code train (pedestal)from reply train amplifier V454B (par. 35c).Each pedestal pulse individually enables tubeV554 to pass an individual pulse from the dif-ferentiator. The resulting reply train of pulsestriggers blocking oscillator V553B once foreach pulse received. The output of blocking os-cillator V553B, consisting of an accuratelytimed reply train, is applied to trigger amplifierV151A in the modulator-transmitter section ofthe receiver-transmitter (par. 37b). The ring-ing oscillator and coincidence card provides therequired pulse spacing accuracy.

b. Driver and Ringing Oscillator (fig. 41).Negative main gate pulses are coupled throughcapacitor C551 and are applied across voltagedivider resistors R551 and R571 to the grid ofdriver tube V551A. Tube V551A is zero-biasedunder static conditions and will accept the fullamplitude swing of the main gate pulse. Theplate of tube V551A is maintained at ac groundby capacitor C552; plate voltage is suppliedthrough resistor R552. Ringing oscillatorV551B is a Hartley-type oscillator and directcathode coupling is used between it and thedriver. Inductor L551 and capacitor C553 formthe parallel-resonant circuit with L551 adjust-able. Tube V551B bias is obtained from cathoderesistor R553. The cathode is connected toground through a tap on inductor L551 to pro-vide feedback to sustain oscillations. Oscillatorplate voltage is supplied directly from the +125-

volt dc bus, and the output signal is taken fromthe parallel-resonant circuit. The negative gatepulse from the cathode or V551A is appliedacross inductor L551, and ringing oscillatorV551B is shock-excited into oscillation. In-ductor L551 is adjusted to produce a one-cycleperiod of 1.45 usec (approximately 690 kc).This oscillator is, and must be, stable as itsoutput provides accurate pulse timing for thetransmitted reply trains.

c. First and Second Clippers (fig. 42). The690-kc ringing oscillator output is direct coupledthrough resistor R554 to first clipper V552A.Positive peak clipping takes place in the gridcircuit of tube V552A because of grid currentflow through resistor R554 on positive peaks.The output of V552A, developed across plateload resistor R555, is coupled through capacitorC554 to the grid of second clipper V552B. TubeV552B clips the positive peaks fed to its gridby plate saturation. Resistor R556 is small andwill not accommodate the full signal swingpresent on the grid. Because of negative biasprovided by resistors R557 and R558, negativegrid peaks drive tube V552B into cutoff. Theoutput of second clipper V552B, developedacross plate load resistor R556 is coupledthrough capacitor C555 to the grid of differen-tiator V553A.

d. Differentiator (fig. 43). The 690-kc squarewave from the plate circuit of second clipperV552B is coupled through capacitor C555 tothe grid of differentiator V553A. The couplingcircuit, consisting of capacitor C555 and re-

Figure 41.

Figure 42.

sistor R560, has a short time constant (approxi-mately 0.056 usec). This short time constantdifferentiates the square wave, applying posi-tive and negative pulses (representing the lead-ing and trailing edges of the 690-kc squarewave) to the grid of V553A. Type V553A ispositive biased to saturation by the voltage di-vider network consisting of resistors R559 andR560. The positive pulses are not amplified,but the full amplitude of the negative pulsesare amplified by tube V553A developing posi-tive pulses at its plate circuit. The plate circuithas coil L552 in parallel with plate load resistorR562. This improves the high-frequency re-sponse and peaks the pulses, giving them ashort rise and decay time and good amplitude.Plate voltage for V553A is supplied from the

52

+125-volt dc source (par. 41e) through a de-coupling filter consisting of resistor R561 andcapacitor C556.

e. Coincidence Detector (fig. 43). The out-put of differentiator V553A, consisting of ac-curately timed (1.45 usec) positive pulses, iscoupled through capacitor C557 to the suppres-sor grid of coincidence detector V554. The pulsereply train from reply train amplifier V454B atpin 1 of card connector P551 is coupled throughcapacitor C559 to the control grid of V554. Thesuppressor grid of the coincidence detector isbiased to cutoff by voltage divider resistorsR565 and R566, and the control grid is biasedto cutoff by voltage divider resistors R563 andR564 connected to the -150-volt dc source (par.42). The presence or absence of pulses in the

AGO 10004A

53

Figure 43.

54

Figure 44.

output is determined by the positive pulses inthe pulse train, which acts as the gating signalfor the coincidence detector. The timing accu-racy is determined by the pulses from the dif-ferentiator. The output of tube V554 startsoperation of blocking oscillator V553B.

f. Blocking Oscillator (fig. 43). The plateof tube V554 is connected in parallel with theplate of blocking oscillator V553B through theprimary of blocking oscillator transformerT551 to + 125-volt dc source (par. 41e). Whenpositive pulses are present on both grids oftube V554 (e above), plate current flowsthrough the primary of transformer T551. Thiscurrent induces a positive voltage at terminal4. The grid of tube V553B was cutoff by a nega-tive bias from the voltage divider consisting ofresistor R567 and Zener diode CR551. Thepositive induced voltage at terminal 4 of trans-former T551 starts the flow of blocking oscilla-tor V553B plate current. This additional cur-rent through the primary of T551 increases theinduced positive voltage applied to the grid,driving tube V553B into saturation. Once tubeV553B is at saturation, the current throughT551 primary stops increasing. At this time,the magnetic field in the transformer starts tocollapse, driving the grid into cutoff. Blockingoscillator V553B is a fully driven oscillator andits pulse output characteristics are determined

by transformer T551 shunted by resistor R573.Only positive pulses are coupled through capaci-tor C558 from cathode resistor R568, becausethe grid of tube V553B is driven to cutoff dur-ing negative portions of the grid pulses. Posi-tive output pulses are prevented from develop-ing across resistor R572 by diode CR552, butexternal positive pulses applied through frontpanel TRIG IN jack J105 will pass to provideexternal triggering of transmitting blockingoscillator V151B (par. 37b).

37. Theory of Modulator-Transmitter(fig. 44)

a. General. The pulse reply train from block-ing oscillator V553B (par. 36f) in the ringingoscillator and coincidence card is applied totrigger amplifier V151A. If the ground connec-tion from control unit switch S904 is present,trigger amplifier V151A amplifies reply trainof pulses and applies them as triggers to block-ing oscillator V151B. Blocking oscillator V151Bgenerates pulses with proper rise time, delaytime, and pulse width as required for the trans-mitted replies. Properly shaped pulses fromV151B are supplied to driver V152. The driveramplifies the pulses and applies them to themodulator. The modulator produces pulses ofsufficient amplitude to excite the transmittingoscillator. The pulses from the modulator arecoupled through pulse transformer T153 to

transmitting oscillator V154. The transmittingoscillator generates a burst of RF energy foreach pulse received. The output of the trans-mitting oscillator, consisting of 1,090 to 1,110mc RF pulses representing the coded pulse replytrain, is applied through the duplexer to theantenna.

b. Trigger Amplifier and Blocking OscillatorV151 (fig. 45). Both sections of trigger ampli-fier and blocking oscillator V151 are biased tocutoff by the -150-volt dc distribution bus(par. 42) through decoupling filter consistingof coil L151 with capacitors C153, C155, andC156. Trigger amplifier grid pin 2 receivesbias from voltage divider resistors R151 andR152. When master control switch S904 onthe control unit is in STBY, resistor R151 isnot grounded, and the full -150-volts is appliedto trigger amplifier grid pin 2. This high biasprevents transmitter triggering during standbyperiods. Capacitor C152 bypasses the lead tothe master control switch. Blocking oscillatorgrid pin 7 is biased by resistor R153 and Zenerdiode CR151. Zener diode CR151 maintainsa constant bias voltage of approximately -30volts dc. A positive pulse applied to the triggeramplifier grid causes plate current to flowthrough the primary of blocking oscillatortransformer T151, and a positive voltage in-duced in the secondary at terminal 2 is appliedto the blocking oscillator grid pin 7. This posi-tive voltage causes the blocking oscillator platecurrent to flow through the primary of trans-former T151, increasing the induced voltageapplied to the blocking oscillator grid. Theblocking oscillator grid rise time is nearly thesame as the rise time of the trigger pulse, sothat the grid draws current almost immediately.This grid current flow charges capacitor C151,with the charge rate determined by the settingof variable resistor R154. (The time constantof C151 and R154 determines the width of theblocking oscillator output pulse.) The blockingoscillator saturates as the trigger pulse ap-proaches maximum amplitude, reducing therate of plate current increase in the primary oftransformer T151. This reduces the trans-former secondary voltage applied to the block-ing oscillator grid. When negative voltageacross capacitor C151 equals the positive volt-age across the transformer secondary, the twovoltages cancel, and the blocking oscillator grid

returns to cutoff. Plate current cutoff causescollapse of the magnetic field of transformerT151, driving the blocking oscillator grid be-yond cutoff. Capacitor C151 discharges slowlyto return grid bias to the static level slowly,preventing the blocking oscillator from beingtriggered by spurious oscillations in its owngrid circuit. During this return to static bias,spurious oscillation amplitudes are too low toswing the oscillator grid positive, but closelyspaced pulses of a reply train have sufficientamplitude to overcome the small additional biasdeveloped by capacitor C151. Blocking oscilla-tor output pulses are taken from secondarynumber two of transformer T151. Plate voltagefor the trigger amplifier and blocking oscillatoris taken from the +300-volt dc distribution bus(par. 41d) through decoupling filter L152 andC157, and through the primary of transformerT151.

c. Driver V152 (fig. 45). Blocking oscillatoroutput pulses are amplified by driver tube V152for application to modulator V153. Positivepulses from transformer T151 are applied toboth parallel driver grids, which are biased be-yond cutoff. This bias of approximately -50-volts is taken from the -150-volt dc circuitthrough a voltage divider consisting of resistorsR155 and R156 with Zener diode CR152. Zenerdiode CR152 maintains this voltage at a con-stant value. When positive pulse voltage over-comes the bias, the driver conducts, amplifyingthe input pulse. Resistors R157 and R158 pre-vent parasitic oscillations in driver tube V152.Resistor R163 shunts the secondary of trans-former T151 to prevent ringing. Output of thedriver is coupled to the modulator throughtransformer T152. Plate voltage for the driveris taken from the +300-volt dc distribution bus(par. 41d) through decoupling filter L152,C157, and C158, and the primary of transformerT152. Pin 3 of transformer T152 secondaryis connected to the -150-volt decoupling filter.This provides negative bias for the grid ofmodulator V153 (d below).

d. Modulator V153 (fig. 46). Driver outputpulses are amplified by modulator V153 toprovide high amplitude positive pulses for theplate of transmitting oscillator V154. Positivepulse voltages from T152 overcome the -150-volt bias on the modulator grid (c above). This

AGO 10004A 55

Figure 45. Trigger amplifier, blocking oscillator, and driver, partial schematic diagram.

bias is well beyond cutoff valve. Positive pulsesapplied to the grid from the secondary of T152cause tube V153 to conduct. The pulsed platecurrent of tube V153 through the primary ofpulse transformer T153 develops pulses of ap-proximately 2,000-volt amplitude across thesecondary. These pulses are applied to thetransmitting oscillator as plate voltage. Platevoltage for the modulator is obtained from the+1,200-volt dc distribution (par. 41b) a n dscreen voltage is obtained from the +600-voltdc distribution (par. 41c).

e. Transmitting Oscillator V154 (fig. 46).Transmitting oscillator V154 generates RFenergy which is coded in bursts, according tothe reply train fed to the modulator. The os-cillator is a lighthouse tube, operating in afolded, full wavelength cavity at 1,090 to 1,110mc. A sliding inductive shunt permits tuningthe cavity. Cathode resistor R162 provides theminimum bias for oscillator V154. Plate voltageis the 2,000-volt pulses from the modulator and

pulse transformer (c above). These pulsesexcite the transmitting oscillator. The RF out-put from the cavity is picked up by the adjust-able capacitive probe and applied through jackJ151 to the coaxial line of the duplexer. ResistorR159 provides a ground return for the second-ary of pulse transformer T153, and developsthe audio monitor output.

f. Duplexer. The duplexer (fig. 116), an-tenna tr switching component part, is made upof three lengths of coaxial cable joined togetherat a tee connection. Two line sections are cri-tical in length (receiver and transmitter); thethird (antenna) is not. The line section betweenthe tee and ANTENNA receptacle J101 is non-resonant; therefore, its length is not critical.A full wavelength line at 1,030 mc (receiverfrequency) is used between the tee and trans-mitting oscillator V154. Because this end isterminated by probe coupling in the oscillatorcavity, the received interrogation signal looksinto an open circuit at the tee. Seven quarter-

56 AGO 10004A

Figure 46. Modulator and transmitting oscillator, partial schematic diagram.

wavelengths of line, at 1,090 mc (transmitterfrequency) are used between the tee and con-verter input connector J102-P102. The receiverline is terminated in a grounded loop and there-fore presents an open circuit to transmittersignal at the tee. Each line is nonresonant toits correct signal.

38. Antenna Theorya. Antenna AT-884/APX-44 is a horizon-

tally polarized, omnidirectional antenna in theform of a small metal blade (fig. 5, TM 11-5895-217-12). Its frequency range is 900 to1,220 megacycles with a low-voltage standingwave ratio. The antenna is fed from a coaxialcable transmission line single 50-ohm coaxialconnector. The single antenna and transmissionline conducts both received interrogations andtransmitted replies.

b. The antenna is a half-wave grounded typefed from close to one end. The half wavelength

is measured along the blade edge from onemounting flange to the opposite flange. In ac-tual practice, the blade junction is insulatedand sealed from the mounting flange with oneend of the blade grounded internally. The co-axial connector feed is connected at a pointaway from the grounded end along the bladethat best matches the 50-ohm coaxial trans-mission line.

c. The antenna is omnidirectional by beingfolded back at the ends and having a compara-tively large metal surface. The large metalsurface also provides the required broadbandcharacteristics. The voltage standing waveratio varies from approximately 1.31:1 to1.27:1 over the receiver-transmitter frequencyrange. The aircraft metallic surfaces forms theground plane against which the antenna radi-ates. The antenna requires no adjustments orservicing at any time.

Section V. POWER SUPPLY AND CONTROL CIRCUITS THEORY

39. Theory of High-Voltage Power Supply volts dc by the high-voltage power supply. This(fig. 47) supply also furnishes 6 volts ac for transmit-

a. General. Aircraft primary power at +27.5 ting oscillator V154 filament. This filamentvolts dc is converted to +1,200, +600, and +300 voltage is obtained from secondary winding

AGO 10004A 57

terminals 10 and 11 of transformer T2, andthrough resistor R13. The high-voltage powersupply consists of power transistors Q3 andQ4; transformer T2; 16 silicon diode rectifiers,CR9 through CR24; associated filter, decoupling,control, and protective circuits.

b. Primary Circuit. Power transistors Q3and Q4 operate as a push-pull, 400-cps square-wave oscillator, to provide a changing primarycurrent in the transformer. Transformer T2primary contains the equivalent of four wind-ings, two are used for voltage transformationand two provide feedback. The input power,+27.5 volts dc, is applied from pin 44 of con-nector J112, through fuse F101 to contacts 2and 4 of power relay K5. Capacitor C9 bypassesany signals present on the +27.5-volt aircraftpower source. When the control unit mastercontrol S904 is turned to STBY, LOW, NORM,or EMER, a ground connection is suppliedthrough pin 22 of connector J112 to pin 2 ofpower relay K5. This causes K5 to energize,applying the input power through the filter con-sisting of coil L1 and capacitors C1 and C2 tothe center tap of transformer T2. This positivevoltage is applied through the primary windingof T2 to the emitters of transistors Q3 and Q4(terminals 2 and 4), The feedback windings(terminals 1 and 5) connect the +27.5 voltson the primary and the regenerative feedbackto the bases of each transistor. When poweris applied, two voltage divider networks, resis-tors R7 and R8 and resistors R9 and R10, areconnected to ground through contacts of relayK7. These networks provide forward bias fortransistors Q3 and Q4 to insure starting cur-rent. Because of tolerance variations in trans-former T2 primary, transistors, and resistors,the two transistor circuits are unbalancedenough so that one transistor will begin toconduct heavily through its half of the primary.Conduction builds up rapidly, aided by the feed-back, until transformer core saturation isreached. When saturation is reached, the pri-mary field begins to collapse, the first transistoris cut off by its feedback winding polarity re-versal, and the second transistor begins con-duction. Its current flows in the oppositedirection through the other half of transformerT2 primary to build up and produce the oppositepolarity half-cycle of required primary squarewave. Thus, each transistor operates as a

switch alternately closing and opening to pro-duce current variations in the primary andpermit a current to be induced in the secondary.When the oscillations begin, the +300-volt sec-tion causes current to flow through relay K7and resistor R15. Relay K7 energizes, remov-ing the ground connection from the startingforward bias circuit. The transistors continueto oscillate with the normal operating bias.

c. Positive 300-Volt Dc Section. One second-ary (terminals 8 and 9) of transformer T2 fur-nishes its induced voltage to a bridge rectifiercircuit consisting of diodes CR9, CR10, CR11,and CR12. Output of this bridge rectifier is+300 volts dc, which is filtered by capacitor C5and fed to the +300-volt dc distribution circuit(par. 41d).

d. Positive 600-Volt Dc Section. The secondsecondary (terminals 6 and 7) of transformerT2 furnishes its induced voltage to diodes CR21,CR22, CR23, and CR24 for rectification. Thesefour diodes are series-connected (to providethe required peak inverse voltage rating) ina half-wave rectifier circuit. Output of thisrectifier, +600 volts dc, is filtered by capacitorC6 and fed to the +600-volt dc distributioncircuit (par. 41c).

e. Positive 1,200-Volt Dc Section. Output ofthe +600-volt dc section secondary of T2 ( dabove) is also fed to a voltage doubler rectifiercircuit consisting of diodes CR13 through CR20and capacitor C8. On one half-cycle, capacitorC8 charges to peak voltage through diodes CR13through CR16. On the next half-cycle, thecharge voltage on C8 adds to the peak voltage ofthe transformer secondary, charging filter ca-pacitors C7 and C12 through rectifiers CR18through CR20. The 1,200-volt dc output of thisrectifier is applied to the +1,200-volt dc distri-bution circuit (par. 41b).

40. Theory of Low-Voltage Power Supply(fig. 48)

a. General. Aircraft primary power, at 27.5volt dc, is converted to +125- and -150-voltdc by the low-voltage power supply. This supplyalso furnishes 115-volt ac for operation ofblower B1. Blower B1 obtains 115 volts ac atapproximately 400 cps from secondary winding(terminals 10 and 11) of transformer T1. This

58 AGO 10004A

Figure 47. High-voltage power supply, partial schematic diagram.

voltage is applied directly to the first field wind-ing (terminals 1 and 4) and through phase-shift capacitor C11 to the second field winding(terminals 1 and 5). The blower is mountedon the front of the receiver-transmitter. Thelow-voltage supply consists of power transistorsQ1 and Q2; transformer T1; eight silicon dioderectifiers, CR1 through CR8; associated filter,decoupling control, and protective circuits.

b. Primary Circuit. Operation of the low-voltage power supply primary circuit is similarto the high-voltage supply (par. 39b). Powertransistors Q1 and Q2 oscillate to provide the

AGO 10004A

changing primary current through transformerT1. The input +27.5 volts is supplied throughthe same filter that applied power to terminal3 of transformer T2. Starting forward bias isprovided by voltage divider resistors R1-R2,and R3-R4 for transistors Q1 and Q2, respec-tively. Relay K6, when deenergized, suppliedthe ground connection for the starting forwardbias circuits. Relay K6 is energized by currentfrom the -150-volt rectifier (d below) throughits coil and resistor R14.

c. Positive 125-Volt Dc Section. One second-ary winding (terminals 6 and 7) of transformer

59

Figure 48. Low-voltage power supply, partial schematic diagram.

T1 provides voltage to a bridge rectifier, diodesCR1, CR2, CR3, and CR4. The output of thisrectifier is +125 volts dc, filtered by capacitorC3, and fed to the +125-volt dc distributioncircuit (par. 41e).

d. Negative 150-Volt Dc Section. A secondsecondary winding (terminals 8 and 9) of trans-former T1 provides voltage to a bridge rectifier,diodes CR5, CR6, CR7, and CR8. The outputof this rectifier is -150-volts dc, filtered bycapacitor C4, and fed to the -150-volt dc dis-tribution circuit (par. 42).

41. B+ Distribution(fig. 49)

a. General. Four

60

B+ distribution circuits

carry B+ power throughout the receiver-trans-mitter. These circuits are supplied with volt-ages from the high-voltage power supply (par.39) the low-voltage power supply (par. 40).The B+ distribution circuits are: +1,200 volts,+600 volts, +300 volts, and +125 volts.

b. Positive 1,200-Volt Distribution Circuit.The +1,200-volt distribution circuit only sup-plies plate voltage to modulator V153 (par.37d) .

c. Positive 600-Volt Distribution Circuit.The +600-volt distribution only supplies screengrid voltage to modulator V153.

d. Positive 300-Volt Distribution Circuit.The +300-volt dc is connected through the

AGO 10004A

filterC157V152lator

consisting of choke L152 and capacitorsand C158 to the plate circuits of driverand trigger amplifier and blocking oscil-V151 (par. 37). This distribution circuit

also applies plate voltage, decoupled by resistorsR103, R104, and R105 and capacitors C103 andC104, to the crystal oscillator and tripler V101in the converter subchassis (par. 26).

e. Positive 125-Volt Distribution Circuit.This distribution circuit supplies plate andscreen voltage to most of the tubes in the re-ceiver-transmitter. The +125-volt dc is dis-tributed

(1)

(2)

(3)

(4)

(5)

as follows:To the IF compressor subchassis (par.27) through pin 5 of connector J203.Within the IF suppressor subchassis,the voltage is applied directly to theplate circuits of first video amplifierand cathode follower V207 and secondvideo amplifier and cathode followerV208. The voltage is also applied toa distribution bus for the six IF ampli-fiers V201 through V206. This busconsists of a series of filters that suc-cessively decouple and apply plate andscreen voltage to each individual IFamplifier. These decoupling filters con-sist of RF chokes L202, L204, L206,L207, L209, and L211 with capacitorsC204, C208, C202, C206, C224, andC229 for IF amplifiers V201 throughV206, respectively.To voltage divider network consistingof resistors R641 and R642 which sup-plies +60-volt dc bias for the diodesin the reply code switching cards(par. 32-34).To trigger amplifier and encoderblocking oscillator plate circuits, gatedamplifier V502 plate and screen cir-cuits, and ring around gate multi-vibrator V503 plate circuits throughpin 11 of blocking oscillator and ringaround card (par. 31) connector P501.To one of three time constant circuitsfor ring around gate multivibratorV503 (par. 31c) through contacts ofrelays K1 and K2.Through pin 4 of video amplifier card(par. 28) connector P301 to the plateand screen circuit of spike suppressor

AGO 10004A

(6)

(7)

(8)

(9)

V301, and the plate circuits of blankedcathode and inverter V302, blankingamplifier and cathode follower V302,and A.O.C. amplifier V304.Through pin 10 of ringing oscillatorand coincidence card (par. 36) con-nector P551 to the plate circuits ofringing oscillator and driver V551,first and second clippers V552, differ-entiator and blocking oscillator V553,and the plate and screen grid circuitsof coincidence detector V554.Through pin 7 of decoder card (par.29) connector P351 to the plate andscreen grid circuits of the modes 1,2, and 3 decoders V351, 352, and V353,respectively.Through pin 11 of mode reply selectorcard (par. 35) connector P451 to theplate and screen grid circuits of themodes 1, 2, and 3 reply selectors V451,452, and V453, and to the plate circuitsof main gate and reply train amplifierV454.Through pin 3 of gate generator card(par. 30) connector P401 to the platecircuits of modes 1, 2, and 3 and maingate multivibrators V401, V402,V403, and V404.

42. Bias Distribution(fig. 50)

The bias distribution circuit supplies -150-volts dc obtained from the low-voltage powersupply (par. 41d) to may stages throughoutthe receiver-transmitter. This bias voltage isdistributed as follows:

a. Through a filter consisting of choke L151with capacitors C153, C155, and C156 to thegrid circuits of modulator V153, driver V152,trigger amplifier and blocking oscillator V151,and tripler V101.

b. Through pin 6 of IF suppressor subchassis(par. 27) connector J203, to the suppressor cir-cuit (grid circuit of second video amplifierV208A).

c. Through pin 10 of video amplifier card(par. 28) connector P301 to the control andsuppressor grid circuits of spike suppressorV301 and to the grid circuits of blanked cathodefollower V302B, blanking cathode followerV303A, and A. O. C. amplifier V304.

61

d. Through pin 9 of decoder card (par. 29)connector P351, to the control and suppressorgrid circuits of modes 1, 2, and 3 decodersV351, V352, and V353.

e. Through pin 7 of ringing oscillator andcoincidence card (par. 36) connector P551, tothe control and suppressor grid circuits of coin-cidence detector V554, and to the grid circuitsof clipper V552B and blocking oscillator 553B.

f. Through pin 7 of mode relay selector card(par. 35) connector P451 to the control andsuppressor grid circuits of modes 1, 2, and 3relay selectors V451, V452, and V453.

g. Through pin 7 of gate generator card(par. 30) connector P401 to the grid circuitsof modes 1, 2, 3, and main gate multivibratorsV401, V402, V403, and V404.

43. Primary Power Distribution(fig. 51)

a. General. Primary power for transponderset operation is obtained from the 27.5-volt dcaircraft power source through the interconnect-ing cable or aircraft wiring to pin 44 of re-ceiver-transmitter connector J112. It is fusedagainst overload by fuse F101 and applied toone coil lead and one contact of power relay K5.Master control switch S904 supplies the groundconnection to the other coil lead, energizingrelay K5.

b. Primary Power Circuits. Relay K5 ap-plies the 27.5-volt dc power to all the primarypower circuits. The primary power is dis-tributed as follows:

(1)(2)

(3)

(4)

62

To the control relays K1 through K4.Through pin 36 of receiver-transmitterconnector J112, and the interconnect-ing cable (or aircraft wiring) to thecontrol unit pilot lamp.Through filament dropping resistorR160, bypassed by capacitor C109, tothe filament of converter oscillatorV101.Through filament dropping resistorR160, bypassed by capacitor C154, toa series-parallel circuit consisting ofthe filaments of trigger amplifier andblocking oscillator V151, driver V152,and modulator V153, with current dis-tribution resistor R161.

(5)

(6)

(7)

(8)

(9)

(10)

(11)

(12)

Through a filter, consisting of chokeL1 and capacitor C1 and C2, to theprimaries of low-voltage transformerT1 and high-voltage transformer T2.Through connector P201--J203, pin 1,to two series filament circuits in theIF suppressor subchassis. The first cir-cuit consists of dropping resistorR237, the filaments of tubes V201through V204, and series decouplingcoils L213, L214, L215, and L220 withbypass capacitors C233 through C240.The second circuit consists of droppingresistor R240, the filament of tubesV205 through V208, and series de-coupling coils L216 through L219 withbypass capacitors C241 through C249.Through pin 14 of card connectorJ551-P551 to the ringing oscillatorand coincidence card series filamentcircuit, consisting of tubes V551through V554, dropping resistor R569,and current distribution resistor R570.Through pin 1 of card connector J501-P501 to the blocking oscillator andring around card series filament cir-cuit, consisting of the filaments oftubes V501, V502, and V503 with drop-ping resistor R519 and current dis-tribution resistor R520.

Through pin 15 of card connectorJ451-P451 to the mode reply selectorseries filament circuit consisting of thefilaments of tubes V451 through V454with series resistor R469 and currentdistribution resistors R470, R471, andR472.Through pin 15 of card connectorJ401-P401 to the gate generator cardseries filament circuit consisting ofthe filament of tubes V401 throughV404 with dropping resistor R425.Through pin 1 of card connector J351-P351 to the decoder card series fila-ment circuit consisting of the filamentsof tubes V351, V352, and V353 withdropping resistor R366.Through pin 1 of card connector J301-P301 to the video amplifier card seriesfilament circuit consisting of the fila-ments of tubes V301 through V304

AGO 10004A

with dropping resistor R319 and cur-rent distribution resistor R320.

44. Control Circuits Block Diagram(fig. 52)

All in-flight operation of the transponderset is controlled by the control unit. Its basicoperation is divided into two groups, functionaland operational controls.

a. Functional Controls. The functional con-trols include master control S904, function con-trol S903, I/P switch S907 (including relaysK901 and K902), AUDIO switch S908, MODE2 switch S905, MODE 3 switch S906, and pilotlamp E901.

(1)

(2)

(3)

(4)

(5)

Master control S904 operates receiver-transmitter power relay to apply- pri-mary power to the transponder set(par. 43), selects either low or nor-mal receiver if sensitivity, and oper-ates receiver-transmitter relay K3 foremergency (EMER) replies.Function control S903 operates re-ceiver-transmitter relays K1 throughK4 to detemine the reply category,and supplies the ground connection forenabling the MODE 1 MODE 3 codecontrols to select their reply trainsfor selective identification feature re-plies (MOD or CIVIL).I/P switch S907 provides two meansof energizing I/P relay K901 eitherdirectly at the control unit or fromthe aircraft microphone (mike) switchcircuits. When relay K901 is ener-gized, it operates through the functioncontrol ((2) above) to provide therepeated replies required for posi-tion identification. I/P time-delayrelay K902 keeps relay K901 ener-gized for approximately 30 secondsafter it has been energized.AUDIO switch S908 applies audio(relay pulses) to the aircraft audiosystem to provide the pilot with ameans of monitoring the transmittedreplies.MODE 2 and 3 switches S905 and S906enable or disableswitching cards.

AGO 10004A

their reply code

(6) Pilot lamp E901 (a press-to-test in-dicator lamp) indicates when thetransponder set is turned on.

b. Operational Controls. The operationalcontrols consist of the MODE 1(S901) and MODE 3 (S902) codecontrols. When these controls are en-abled by the function control (a(2)above), they control the switchingdiodes in the mode 1 and mode 3 replycode switching cards to determine thecomposition of their respective codedreply trains.

45. Master Control Circuits(fig. 53)

a. STBY Position. Contact X2 of switchS904A applies a ground to the coil of powerrelay K5 which energizes and applies +27.5volts dc throughout the transponder set (par.43). All circuits are activated after warmupexcept trigger amplifier and blocking oscillatortube V151 (par. 37b), which has the full -150-volt dc bias applied to grid pin 2. Contact Y2of switch S904B sets the receiver to high sen-sitivity by shorting resistor R226 to ground,but the reply train of pulses fed to tube V151cannot pass because of the high cutoff bias.

b. LOW Position. Rotating switch S904 tothe LOW position permits contact X3 of sectionA to hold relay K4 energized. Contact Y3 ofsection B, having no connection, places the re-ceiver on LOW sensitivity by adding resistorR226 to the cathode circuits of first and secondIF amplifiers V201 and V202. Contact X3 ofsection B ground one end of resistor R151 toreduce the cutoff bias on V151. This allowsV151 to amplify the reply pulses that are tobe transmitted.

c. NORM Position. Switch S904 in theNORM position selects high receiver sensi-tivity by grounding resistor R226 through con-tact Y4 of switch section B. Contact X4 ofsection B maintains normal operating bias ontube V151 and contact X4 of section A holdsrelay K5 energized.

d. EMER Position. Depressing the barrierbutton on the control unit and setting mastercontrol S904 to EMER position, close emer-gency-modified relay K3 and emergency-normalrelay K4 if normal codes are in use. Contact

63

64

Figure 52.

Y5 of section A supplies this ground to relayK3. Contact X5 of section A holds relay K5energized; contacts X5 and Y5 of section Bmaintain normal operating bias on tube V151and high receiver sensitivity, respectively. Theoperation of relays K3 and K4 is discussed inparagraph 46d and g.

46. Function Control Circuits(fig. 53)

a. General. The following discussion appliesonly to the circuitry which prepares the re-ceiver-transmitter for operation in a particularcategory. Actual code formations are coveredin paragraphs 32, 33, and 34.

b. NORMAL Functions. When function con-trol S903 is set to NORMAL position, contactX1 of S903B closes normal relay K1. The clos-ing of relay K1 is a preparatory step for mode1 and mode 3 emergency and identification ofposition operation. The MODE 1 and MODE 3code controls are disabled as no ground is ap-plied to contacts X2 or X3 and Y2 or Y3 ofS903B. Therefore, no reply code is obtained;mode 1 and 3 replies consist of only the O-usecpulse (present in all replies). Mode 2 repliesrequire a second pulse spaced 15.95 usec afterthe O-usec pulse. This pulse is provided by con-tacts 6 and 8 of relay K1. These contacts re-move the +60-volt dc bias applied to switchingdiode CR661 in the mode 2 reply code switch-ing card, allowing the 15.95-usec pulse fromdelay line DL601 to be developed across resistorR670. Capacitor C671 couples this pulse to mode2 reply selector V452.

c. NORMAL-I/P Functions. Switches S903and S904 remain as in b above for I/P oper-ation, and switch S907 is set to one of two posi-tions. If I/P is selected (spring return side),a ground is supplied to the coil of I/P controlrelay K901 and to the heater of the time-delayrelay K902. When relay K901 energizes, hold-ing contacts 4-5 and 6-8 close. Relay K901 willremain energized until time-delay relay K902contacts 5-7 open (approximately 30 seconds)removing the +27.5 volts dc. Contacts 9-10and 12-13 apply a ground connection througharm Y of switch S903A and contact Y1 to ener-gize I/P relay K2. The second pulse neededfor all NORMAL-I/P replies is supplied bycontacts 9-10 of relay K2 and 12-13 of relayK1. These contacts provide the ground con-

nection to close switching diode CR627 whichapplies the 15.95-usec pulse to mode 1 replyselector V451 bus. Contacts 6-8 of relay K2energize modified-emergency relay K3. WhenK3 is energized, its contacts 9-10 will ener-gize emergency-normal relay K4. Mode 1 replyselector V451 will produce the two pulses for allmodes of interrogation because all-mode de-coder output switching diode CR354 has beenclosed by contacts 9-10 of relay K4. The ringaround circuitry has been activated during thistime, but gated amplifier V502 could not con-duct because of the lack of a suppressor grid15.05-usec pulse. (The ground connection fromcontacts 9-10 of K2 was removed from con-tacts 4-5 of relay K1 when relay K2 energized).

d. NORMA L-EMER Functions. DuringNORMAL-EMER operation, relay K1, K3, andK4 are energized to provide repeated replytrain operation. Contacts 9-10 of relay K3,energized by contact 4-5 of S904A, energizesK4 are energized to provide repeated replyK2 close switching diode CR626, which suppliesthe 15.05-usec pulse to gated amplifier V502suppressor grid. Contacts 9-10 of relay K1 sup-ply +125-volts dc to resistor R512, causingring around gate multivibrator to produce a57-usec gate pulse. This gate pulse activatesgated amplifier V502 because its bias has beenreturned to normal by relay K3 contacts 4-5grounding resistor R507. Thus, after the firstdecorder interrogation pulse, the 15.05-usecpulse will trigger the encoder blocking oscilla-tor and produce another pulse spaced 16 micro-seconds after the first. This process is repeateduntil the fourth pulse has been produced. All-mode decoder switching diode CR354 (closedby contacts 9-10 of relay K4) permits all threedecoder outputs to trigger the ring around cir-cuitry.

e. MOD Functions. The last framing pulse(fig. 5) required for all reply trains in MODcategories is continuously supplied to its re-spective mode reply selector as follows: mode1, by contact Y2 of switch S903B and switch-ing diode CR629; mode 2, by contacts 6-7 of de-energized relay K1 and switching diode CR664;and mode 3, by contact X2 of switch S903Band switching diode CR695. Although ringaround gate pulses and gated amplifier pulsesare being generated, gated amplifier V502 is

AGO 10004A 65

held inoperative by open contacts 4-5 of relayK3. The zero time or first framing pulse isalways present, MODE 1 and MODE 3 codecontrols and mode 2 and 3 reply selector V452are enabled by contacts X2 and Y2 of S903B.

f. MOD-I/P Functions. Relay K2 is ener-gized for 30 seconds the same as in c above bycontact Y2 of switch S903A, and relay K3 isenergized by closed contacts 6-8 of relay K2.Ring around gate multivibrator V503 developsa 37-usec gate as determined by the applicationof +125 volts dc to resistor R511 through closedcontacts 10-11 of relay K1 and 4-5 of relay K2.Normal bias is established for the control gridof gated amplifier V502 by closed contacts 4-5of relay K3. Contact X2 of switch S903A willclose 23.85-usec switching diode CR630, whichsupplies the ring around suppressor grid pulseto tube V502. The 23.85-usec ring around pulseplus circuit delays cause the first framing pulseof the second reply train to appear 4.35 usecafter the last framing pulse of the first replytrain (fig. 5). Mode 2 interrogations will notproduce a ring around gate pulse because onlymodes 1 and 3 decoder outputs are availableto trigger the ring around gate multivibratorV503. This change in because contacts 6-8 ofenergized relay K3 have closed diodes CR355and CR356 only. (Relay K4 is not energizedbecause switch S904B contact X1 is open inMOD position).

g. MOD-EMER Functions. Setting switchS904 to the EMER position energizes relayK3 (relays K1, K2, and K4 are deener-gized); contacts 4-5 provide normal bias for

gated amplifier V502; and contacts 6-8 closeswitching diodes CR355 and CR356 to permitmode 1 and mode 3 interrogations to triggerring around gate multivibrator V503. Mode2 interrogations do not require repeated replytrains in EMER operation. The only signi-ficant change from MOD-I/P operation in fabove is that relay K2 is not energized, contacts10-11 of relay K1 and 3-4 of relay K2 now sup-ply +125-volts dc to resistor R513. Ring aroundgate multivibrator V503 produces an 87-usecgate for gated amplifier V502. This allowsenough time for four complete reply trainsspaced 4.35 usec apart (fig. 5).

h. CIVIL Functions. Setting function con-trol S903 to the CIVIL position makes no signi-ficant change from MOD position discussed ine above.

i. CIVIL-I/P Functions. Setting functioncontrol S903 to the CIVIL position for I/Pcategories does not energize relay K2, but ap-plies the ground from contact Y3 of section Adirectly to close 24.65-usec switching diodeCR696 in mode 3 reply code switching card.Because only a mode 3 interrogation will acti-vate mode 3 reply selector V453, the singlepulse spaced 4.35 usec after the last framingpulse will be added to the reply train in mode3. Modes 1 and 2 will produce the normal singlereply train in CIVIL-I/P.

j. CIVIL-EMER Functions. In CIVIL-EMERcategories, relay K3 is energized by contact Y3of switch S904A and operation is identical withMOD-EMER operation (g above).

66 AGO 10004A

CHAPTER 3

T R O U B L E S H O O T I N G

Section I. GENERAL TROUBLESHOOTING TECHNIQUES

Warning: Dangerous voltages exist in Radar Receiver-Transmitter RT-494/APX-44. Takeadequate precautions against electrical shock during troubleshooting. Remove power input priorto making physical contact with parts in the receiver-transmitter.

47. General Instructions

The troubleshooting procedures in thismanual are provided for the levels of mainten-ance shown in the maintenance allocation chart,TM 11-5895-217-12. Systematic troubleshoot-ing procedure includes operation and organi-zational maintenance instructions contained inTM 11-5895-217-12, preventive maintenanceprocedures in chapter 1, and the sectionalizing,localizing, and isolating techniques in para-graphs to follow. Section II provides interunittroubleshooting procedures (including AntennaAT-884/APX-44. and transponder Set ControlC-2714/APX-44), and sections III and IV de-scribe intraunit (within unit) localizing andisolating procedures for Radar Receiver-Trans-mitter RT-494/APX-44.

48. Organization of Troubleshooting Procedures

a. General. The first step in servicing a de-fective transponder set is to sectionalize thefault. Sectionalizing the fault means tracingit to a major component or subassembly. Thesecond step is to localize the fault to a stagewithin the major component or subassembly.The third step, isolation, is sometimes accom-plished by visual inspection for burned-outtransformers, resistors, and arcing, but usuallyrequires voltage and resistance measurementsfor completely isolating the defective part. Forintermittents and part value changes, part sub-stitution is recommended.

b. Sectionalization. The transponder set con-sists of the following three major components:the receiver-transmitter, the control unit, andthe antenna. Sectionalizing the faults in thisequipment first requires determining whichmajor component is defective.

AGO 10004A

(1)

(2)

(3)

(4)

Troubles within the control unit orthe receiver-transmitter must be sec-tionalized to the subassembly or thecircuit section.

The antenna has no subassemblies.

The control unit has two sections:functional control circuits and opera-tional control circuits.

The receiver-transmitter has the fol-lowing removable subassemblies:

(a)(b)(c)(d)(e)(f)(g)

(h)

(i)(j)

Converter subchassis.IF suppressor subchassis.Video amplifier card.Decoder card.Gate generator card.Mode reply selector card.Blocking oscillator and ring aroundcard.Ringing oscillator and coincidencecard.Modulator-transmitter.Power supplies.

(5) Tracing a fault to a major componentis usually accomplished by the func-tional check (par. 14) or interunittroubleshooting (sec. II).

(6) A visual inspection will sometimes re-veal the causes of trouble withouttesting the circuits or taking measure-ments. Broken wires, bent or damagedconnector pins, loose electrical con-nections, and burned or damaged partscan be located by a visual inspection(par. 8 and TM 11-5895-217-12).

c. Localization. With the trouble traced toa major component or subassembly, the nextstep is to determine which stage of the compo-

67

nent or subassembly is defective. The followingtests will prove helpful in localizing the trouble:

(1)

(2)(3)

(4)

(5)

B+ and bias short-circuit check (par.54).Signal tracing (par. 58a).Voltage and resistance measurements(par. 58d and e).Troubleshooting charts (pars. 59, and62 through 72).Intermittent troubles should not beoverlooked as a possible source of dif-ficulty. Intermittents are generallyeither short- or open-circuit troublesthat do not appear until the equipmenthas run for some time or is subjectedto vibration. Intermitted troublessometime may be made to appear bytapping or jarring the unit or by ap-plying heat to a suspected component.

d. Isolation. When trouble has been localizedto a stage, the following techniques will isolatethe faulty part:

(1) Take voltage and resistance measure-

Test equipment

Uhf Signal Generator, Hewlett-Packard Model 612Aor equivalent.

Generator, Electronic Marker AN/USM-108.ªPower Bridge, Polytechnic Research and Development

Inc. (PRD) type 650B or equivalent.b

Bolometer, PDR Type 631-D or equivalent.b

Bolometer Mount PRD Type 628-A or equivalent.b

Coaxial Tuner PRD type 327 or equivalent.Detector, PRD Type 612A or equivalent.Attenuator, PRD Type 756A-10 or equivalent.Coaxial Directional Coupler, Narda Microwave Corp.

Type 3002-20 or equivalent.Wavemeter FXR Co. Inc. Model N410A.Slotted Line, Hewlett-Packard model 805A or equiv-

alent.Standing Wave Indicator, Hewlett-Packard model 415B

or equivalent.Oscilloscope AN/USM-81.Pulse Generator Set AN/UPM-15.Test Set, Electron Tube TV-2/U.Test Set, Electron Tube TV-7/U.Multimeter AN/URM-105.Electronic Multimeter TS-505/U.

Crystal Rectifier Test Set TS-268/U.Test Set, Transistor TS-1100/U.Test Set, Radar AN/UPM-98Power Supply PP-1104A/G or equivalent.

(2)

(3)

ments at the tube sockets and comparethe readings obtained with the valuesshown in the diagrams provided inthis manual.If the voltages are abnormal and theresistances are normal, check the tubeswith the tube tester or by substitution.Examine the printed circuits, if ap-

(4)

49. Test

plicable, with a magnifying glass anda strong light for hairline cracks andevidence of dielectric breakdown.Check the waveforms surrounding thedefective stage for indications whichpoint directly to the faulty part.

Equipment, Materials, and Tools Re-quired

a. Test Equipment. The following chart liststhe test equipment required for troubleshootingTransponder Set AN/APX-44, including theappropriate technical manuals and the assignedcommon names. The characteristics of com-merical test equipment required are listed ind below.

Reference

TM 11-6625-219-12TM 11-1177TM 11-2661TM 11-5080TM 11-6625-203-12TM 11-5511

TM 11-1242

TM 11-5126

Common name

Uhf signal generator

Marker generatorPower bridge

BolometerBolometer mountCoaxial tunerDetectorAttenuatorDirectional coupler

WavemeterSlotted line

Standing wavemeter

OscilloscopePulse generatorTube tester (5th echelon)Tube testerMultimeterVacuum tube voltmeter

(vtvm).Diode testerTransistor testerTest set28-volt supply

~ Use Time-Mark Generator, Tektronix Inc. Type 180A or equivalent until AN/USM-108 is available.* May be replaced by Bridge, Summation AN/USM-68 if available.

68 AGO 10004A

b. Materials. Following is a list of materialsrequired for troubleshooting the transponderset.

Description

UG-710A/U Coaxial Connector(2 rqr).

UG-273/U Adapters (5 rqr) ------

UG-201/U Adapters . . . . . . . . . . . . .

Interconnect cable for connectingthe control unit to the receiver-transmitter (fig. 3).

Rotary coaxial switches (3) (Dan-bury Knudsen, Inc. type CS400or equivalent.

60 feet RG-62/U Coaxial Cable----10 feet RG-8/U Coaxial Cable _____10 feet RG-58/U Coaxial Cable----21 feet RG-21/U Coaxial Cable----UG-57B/U Coupling Adapter --------UG-274/U Tee Adapter

(1 required).UG-88/U Coaxial Connectors

(26 rqr).UG-21/U Coaxial Connectors

(6 rqr).Metal box 2 x 2 x 2 inches100-ohm, 1-watt carbon resistor

Common name

C connectors.

BNC to UHFadapters.

BNC to Nadapters.

Bench test cable.

Bench test switches(S4, S5, and S6).

Video cables.Rf cable.Rf cable.Lossy line.Coupling adapter.Tee adapter.

BNC connecters.

N connectors.

c. Tools. All of the tools required for trouble-shooting and maintenance of the transponderset are included in Tool Equipment TE-113.

d. Test Equipment Characteristics.(1)

(2)

(3)

Uhf signal generator, model 612A.This standard uhf signal generator hasa frequency range from 450 to 1,230mc. The output variable is from 0 to-127 dbm.Marker generator, type 180A. Thismarker generator produces pulsemarkers with spacings from 1 usecto 1 second. The markers are usedto provide one common triggeringsource for all equipments and timingmeasurements.Power bridge, type 650B. The power

(4)

(5)

(6)

bridge measures the output of thetransponder set when coupled to bol-ometer 631-D/628-A and coaxialtuner 327 up to 100 milliwatts averagepower. The frequency range of theentire power output measuring setupis 1,000 to 10,000 mc.

Detector, type 612A. The detector isdouble tuned, with a frequency rangefrom 500 to 10,000 mc. Its voltagestanding wave ratio is less than 1.5:1for all frequencies when terminatedin a 50-ohm nominal line impedance.

Directional coupler, type 3002-20.This is a broadband coaxial directionalcoupler with maximum (max) voltagestanding wave ratio of 1.15:1 over afrequency range from 950 to 2,000 mc.The forward power rating is 2,000watts, the reverse power rating is 20watts, and the peak power rating is10 kilowatts. Coupling directivity is20 db ±1.

Wavemeter, model N410A. The wave-meter is continuously tunable from1,000 to 4,000 mc ±2 percent coaxialtype for measuring the transmitterfrequency.

(7) Attenuator, type 756A-10. This is acoaxial attenuator with fixed attenua-tion of 10 db. It has two N-type con-nectors, a male on one end and a fe-male on the other.

(8) Slotted line, model 805. This is anadjustable slotted 50-ohm coaxial linefor measuring the voltage standingwave ratio on the coaxial antennacables; that transmits RF signalswithin the frequency range of 500 to4,000 mc.

(9) Standing wave indicator, model 415B.This indicator operates with theslotted line ((8) above) to provide adirect meter indication of voltagestanding wave ratio.

AGO 10004A 69

Section II. INTERUNIT

50. Troubleshooting Procedure

Interunit troubleshooting consists of thirdechelon (in-aircraft) troubleshooting only.These procedures are based on anticipated pilotor periodic check reports, and will assist themaintenance personnel to determine which ofthe major units is defective. Because of thecontrol circuit complexity, control unit trouble-shooting is combined and completed in inter-unit procedures, and receiver-transmittertroubleshooting is contained in sections III andIV. Repair references for the antenna areeliminated in paragraph 51 as it is not a re-pairable unit. The interunit troubleshootingchart (par. 51) and the control unit continuitychart (par. 52) involve continuity measure-ments with Multimeter ME-77/U (part ofMultimeter AN/URM-105) in most cases. Usethe X1 OHMS scale for continuity checks and

Item

1

2

3

4

Indication

Transponder set will not energize--

Improper master control

Improper function control

Improper I/P operation ___________

TROUBLESHOOTING

the X10K OHMS scale for short tests. Inter-connecting cable continuity and short test aremade at mounting receptacle J112 with thereceiver-transmitter removed. A ground shouldbe applied to each wire as indicated by theswitch position and X in the box of the chartsin paragraph 52. When short-circuit checksare made, the switches must be rotated to ablank-box position or the control unit connectormust be disconnected from receptacle J901.

51. Interunit Troubleshooting ChartThe chart below lists potential troubles in

the Indication column. Pilot reports may indi-cate only part of the trouble as they may nothave had cause to use other functions of thetransponder set. Before proceeding with thischart, perform the periodic functional check(par. 14) to insure that the extent of thetrouble is known.

Probable trouble

No power input ------------------Fuse blown - - - - - - - - - - - - - - - - - - - - - -Defective interconnect cable -------

Defective master control S904-------

Defective receiver-transmitter -----Defective interconnect cable --------

Defective master control S904-----

Defective receiver-transmitter -----Defective interconnect cable --------

Defective function control S903----

Defective receiver-transmitter -----Defective interconnect cable _______

Defective control unit _____________

Procedure

Check aircraft power source.Replace fuse F101.Check continuity at pin 22 of

mounting receptacle J112 (figs.105 and 133).

Check control continuity in STBYLOW, NORM, and EMER (par.52a).

Replace receiver-transmitter.Check for continuity and shorts,

mounting receptacle J112 pins21, 22, 23, 25, and 32 (figs. 105and 133).

Check master control continuity(par. 52a).

Replace receiver-transmitter.Check for continuity and shorts,

mounting receptacle J112 pins8, 9, 10, 11, 12, and 13 (figs. 105and 133).

Check function control continuity(par. 52b).

Replace receiver-transmitter.Check for continuity or shorts,

mounting receptacle J112 pins14, 24, and 36 (figs. 105 and133).

Check continuity of function con-trol S903A, segment Y (par.52b).

Check relays K901 and K902 (fig.94).

70 AGO 10004A

Item

5

6

78

9

10

11

Indication Probable trouble

MODE 1 and MODE 3 code controlsinoperative.

MODE 1 codes incorrect --------------

MODE 2 codes incorrect ----------MODE 3 codes incorrect -----------

Transponder set weak and/or inter-mittent, all operations.

No audio output -----------------------

Transponder set causes inter-ference in other equipment orequipments.

Defective receiver-transmitter----Defective control unit ------------

Defective interconnect, cable ------

Defective MODE 1 code controlS901.

Defective receiver-transmitter----------Defective receiver-transmitter----------Defective interconnect cable ----------

Defective MODE 3 code controlS902.

Defective receiver-transmitter---------Defective antenna to receiver-trans-

mitter coaxial cable.

Defective antenna -------------------------

Low aircraft bus voltage ---------------

Defective receiver-transmitter---------Defective interconnect cable --------

Defective control unit -----------------

Defective aircraft audio distribu-tion system.

Defective receiver-transmitter---------Defective interconnect cable ----------

Defective receiver-transmitter---------Defective primary power input

filter to transponder set (ifused).

Defective installation or equipmentin which interference occurs.

Procedure

Check switch S907 and pin P ofreceptacle J901 (fig. 121).

Replace receiver-transmiter.Check continuity of common ground

supplied to code controls by func-tion control (fig. 121).

Check for continuity or shorts,mounting receptacle J112 pins11, 15, 16, 17, 18, 19, 20, and 32(par. 52c and figs. 105 and 133).

Check continuity of control (par.52c).

Replace receiver-transmitter.Replace receiver-transmitter.Check for continuity and shorts,

mounting receptacle pins No. 1through 8 (par. 52c and figs. 105and 133).

Check continuity of control (par.52d).

Replace receiver-transmitter.Inspect for mechanical damage to

cable and connectors.Check for continuity and shorts in

cable.Bench test receiver-transmitter

(par. 9), then functional checkwith test hat (par. 14), comparesensitivity and decoding. If low,replace Antenna AT-884/APX-44.

Adjust aircraft bus voltage to 27.5volts dc.

Replace receiver-transmitter.Check for continuity and short,

mounting receptacle J112 pin 35(figs. 105 and 133).

Check AUDIO switch S908, recep-tacle J901 pins S and T, for con-tinuity with switch at ON (fig.121).

Troubleshoot aircraft audio distri-bution systems.

Replace receiver-transmitter.Inspect installation for broken or

damaged wire shields and/orgrounds. Refer to the applicableaircraft technical manual.

Replace receiver-transmitter.Replace filter. (See aircraft instal-

lation diagram.)

Replace or troubleshoot applicableequipment or equipments.

AGO 10004A 71

52. Control Unit ContinuityThe charts in a through d below are subdivided by controls as follows: master control S904,

function control S903, MODE 1 code control S901, and MODE 3 code control S902. The remainingswitches and lamp are not shown because of their simplicity; refer to figures 120 and 121 forwiring details of all switches. Figures 33, 35, and 53 will also be of assistance in correlatingchart information for troubleshooting. All continuity measurements are taken with MultimeterAN/URM-105 set to X1 OHMS scale, and are from pin indicated to chassis ground.

a. Master Control S904 Continuity Chart.

MountingMaster control S904 setting

Control unitreceptacleP112, pin

receptacleJ901, pin OFF STBY LOW NORM EMER

21 F X X X22 H X X X X23 X X X25 J X32 N X X X X X

Note. X denotes continuity; blank space denotes an open circuit.

b. Function Control S903 Continuity Chart.

MountingreceptacleP112, pin

Function control S903 settingControl unit

receptacleJ901, pin NORMAL MOD CIVIL

81112131424

XX

h Xg Xf X (K901 closed) X (K901 closed)E

XX

X

X (K901 closed)

Note. X denotes continuity; blank space denotes an open circuit.

c. MODE 1 Code Control S901 Continuity Chart (Note 2).

Mounting Control unitreceptacle receptacleP112, pin J901, pin

MODE 1 code control S901 setting

Tens (S901A) Units (S901B)

0

xxx

x

1 2

xxx

x

x

3 6 74 5

111315161718192032

xxx

xx

x

xxx

xxx

xxxx

x

xxxxx

x

xxx

x

x

xxxx

x

x

xxx

x

xxxxxx

x

xxx

x

x

xxx

xx

Notes:1. X denotes continuity, blank space denotes an open circuit.2. All continuities are measured with function control in MOD or CIVIL except pins 15 (M) and 32 (N), which

are continuous grounds.

72 AGO 10004A

d. MODE 3 Code Control S902 Continuity Chart (Note 2).

MODE 3 code control S902 setting

Control unitreceptacle Tens (S902A)J901, pin

MountingreceptacleP112, pin

Units (S902B)

3 4 5

BYZWVUXj

12345678

Notes:

1. X denotes continuity; blank space denotes an open circuit.

2. All continuities are measured with function control in MOD or CIVIL except pin No. 1(B), which is a con-tinuous ground.

Section III. RADAR RECEIVER-TRANSMITTER RT-494/APX-44 TROUBLESHOOTING

the nature of the abnormal symptomsis not known.When abnormal symptoms reportedfrom the pullout and functional checksin chapter 1 indicate possible powercircuit troubles.When interunit troubleshooting pro-

53. Receiver-Transmitter Troubleshooting Proce-dure

The procedures given in this section willassist third echelon maintenance personnel inlocalizing troubles within the receiver-trans-mitter. The data is coordinated with informa-tion obtained in section II and/or results ofperiodic checks performed in chapter 1. Be-cause of the numerous internal signal paths,signal tracing is the best method of trouble-shooting to determine the full extent of thetroubles. The block diagram (fig. 8) should beused as a guide to signal distribution andtrouble localization. Figures 54 and 55 providetube and card location information necessaryfor locating major sections of the receiver-transmitter. Figure 6 (front panel) shows fuseand switch location.

54. Checking Primary Power, B+, and Bias Cir-cuits

a. When to Check. When any of the follow-ing conditions apply, check for short or opencircuits and clear the trouble before applyingthe power.

(1) When the receiver-transmitter is beingserviced apart from the other com-ponents of the transponder set and

(2)

(3)cedures in paragraph 51 indicatepossible power supply troubles.

b. Conditions for Tests. To prepare for theshort-circuit tests, perform the following steps:

(1)

(2)

(3)

(4)

Make sure that the receiver-trans-mitter is not connected to the controlunit or the test equipment.Remove both side covers from thereceiver-transmitter.Remove all plug-in components (tubes,printed circuit cards) (figs. 54 and55).Remove transistors Q1 through Q4(fig. 55).

c. Procedure. Perform the resistance meas-urements indicated in the chart (d below) tocheck the power distribution circuits. If ab-normal readings are obtained, make the addi-tional checks outlined. When the defective partis found, repair the trouble beforepower to the receiver-transmitter.

applying

AGO 10004A 73

74

Figure 54.

75

Figure 55.

d. Power Circuit Checks.

Point of measurement

Junction of L1 and C1 and C2 (f ig105 ) .

Positive lead of meter to the junctionof CR1 and CR2 (fig. 109), negativelead to ground.

Negative lead of multimeter to pin 1of K7 (f ig. 106), positive lead tog r o u n d .

Negative lead of multimeter to the topof capacitor C6 (fig. 106), positivelead to ground.

Negative lead of multimeter to V153plate cap lead (f ig. 105), positivelead to ground.

Positive lead of multimeter to the bot-tom lead of CR7 (fig. 105), negativelead to ground.

Normal indication_ — — - - - - -

Approximately 300 ohms resistance.

Approximately 10K ohms.

approximately 80K ohms.

Infinite resistance.

Infinite resistance.

80K ohms resistance.

Isolating procedure

If the resistance is less than 100 ohms,check capacitors C1, C2 (f ig. 105),and C154.

If the resistance is approximately 100ohms, check C109 (fig. 98).

If the resistance is zero, check capaci-tor C3 (fig. 105).

If the resistance is low, check for ashorted rectifier CR1, CR2, CR3, orCR4 (figs. 105 and 109).

If the resistance is high, check for anopen rectif ier CR1, CR2, CR3, orC R 4 .

If the resistance is low, check for as h o r t e d c a p a c i t o r C 5 ( f i g . 1 0 6 ) ,C157, or C158.

If the resistance is low, but at least3 K o h m s , c h e c k f o r a s h o r t e dcapacitor C102, C103 (fig. 99), C104( f i g . 9 8 ) o r r e c t i f i e r C R 9 , C R 1 0 ,CR11, CR12 (fig. 109).

If the resistance is high, check for anopen relay K7 coil, resistor R15 (fig.107) or coil L152 (fig. 106). Checkfor an open resistor R103, R104 (fig.99), R105 (fig. 98), or rectifier CR9through CR12.

Check for a shorted capacitor C6 orshorted rec t i f i e r s CR21 throughCR24 (figs. 106 and 109).

Check for a shorted capacitor C7 (fig.106) or C12.

Check for a shorted capacitor C4 (fig.105), C105 (fig. 98), C153, C155, orC156.

55. Test Setup

The test setup in paragraph 9 may be used for third echelon or preliminary receiver-transmittertroubleshooting, but the equipment listed in paragraph 49 will be necessary for most of the fourthand fifth echelon troubleshooting procedures. Figure 58 illustrates the test equipment connections.Cable fabrication information is included below.

a. Cables. The bench test cable is required to interconnect the control unit and the receiver-transmitter. (See par. 9 for fabrication.) Fabricate the coaxial cables with the connectors listedin the chart below. Refer to figures 56 and 57 for connector installation procedures.

Cable No. Cable(fig. 58) type Length

1 R G - 6 2 / U 6 ft2 R G - 6 2 / U 6 ft3 R G - 6 2 / U 6 ft4 R G - 6 2 / U 6 ft5 R G - 6 2 / U 6 ft

Connectors

2 UG-88 /U2 UG-88 /U2 UG-88 /U2 UG-88 /U2 UG-88 /U

Adapters

1 UG-273/U.1 UG-273/U.

None.1 UG-273/U.

None.

AGO 10004A76

Cable No.(fig. 58)

6789

1 01112131415

Lossy line

Cabletype

R G - 6 2 / UR G - 6 2 / UR G - 6 2 / UR G - 6 2 / UR G - 8 / UR G - 6 2 / UR G - 5 8 / UR G - 5 8 / UR G - 5 8 / UR G - 8 / U

R G - 2 1 / U

Length

6 f t6 ft6 ft6 ft6 ft6 ft6 ft2 ft2 ft3 ft

21 ft

b. Detector Load. A small metal box, 2 b y2 by 2 inches, is used to house a 100-ohm,l-watt carbon resistor for terminating coaxialdetector type 612A. Drill a 1/4-inch hole,centered, in opposite sides of the box. Strip theinsulation from cable No. 9 (about 1 inch)approximately 5 inches from one end. (Leaveenough shield braid to permit attachment tothe box.) Insert the modified portion throughthe box and fasten the shields to the box(solder preferred). Attach the 100-ohm re-sistor from the center conductor of the coaxialcable to the shield or box, and then install theUG–88/U connectors on both ends of the cable.

c. Test Setup Connections. Connect all cablesas shown in figure 58, including switches S4,S5, and S6. Mount the switches in a box or ona panel and placard the positions as shown;also placard the reference designations. Theprobe cables, included with Oscilloscope AN/USM–81, will be used to measure waveformsat the test points after preliminary checks aremade.

56. Test Equipment Calibration

After fabrication, several portions of thetest setup (fig. 58) must be calibrated to de-termine the loss or time delay present. Alltest equipment should be checked for calibra-tion. Follow the procedures given in themanuals provided with the test equipment.

a. Pulse Generator, Pulse Separation Ad-justment. Unless otherwise specified, the pulsegenerator shall be operated with internaltriggering. Where extreme accuracy is desired,the marker generator is used to trigger the

AGO 10004A

Connectors

2 UG-88 /U2 UG-88 /U2 UG-88 /U2 UG-88 /U2 UG-21B/U2 UG-88 /U2 UG-88 /U2 UG-88 /U2 UG-88 /U1 UG-21B/U1 UG-710A/U1 U G 2 1 B / U1 UG-710A/U

Adapters

1 U G - 2 7 3 / U .1 U G - 2 7 3 / U .

None.(b. b e l o w ) .

None.None.

1 U G - 2 0 1 / U .1 U G - 2 0 1 / U .1 U G - 2 9 / U .1 U G - 2 0 1 / U .

None.None.

pulse generator. The procedures listed belowshall be used to calibrate output pulse char-acteristics for accurate interrogation (trigger-ing) of the receiver-transmitter.

(1)

(2)

Disconnect cables No. 4 and No. 6(fig. 58) from switch S6, and recon-nect cable No. 6 to UG–274/U at pulsegenerator OUTPUT. Disconnectcable No. 7 from oscilloscope CHAN-NEL B and reconnect cable No. 4 toCHANNEL B input. Turn on thepulse generator, the marker genera-tor, and the oscilloscope.The test equipment control settingslisted in the charts below are criticalsettings; those not listed shall be ad-justed as required to obtain usableindications. Do not change the pulsegenerator settings during trouble-shooting and final testing unless in-structed to do so in tests.

Oscilloscope control Position

HORIZONTAL DISPLAY_ _ _ _ _ _ _ _ _MAIN SWEEPDELAYED.

MAIN SWEEP TIME/ CM_ _ _ _ _ _ _ _1 MICRO SECMODE_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ALTERNAT E

Marker generator control Position

TRIGGER RATE control_ _ _ _ _ _ _ _ _1 KCMARKER control_ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 USEC

Pulse generator control Position

SYNC selector knob _ _ _ _ _ _ _ _ _ _ _ _ EXT GOING +SYNC switch _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ LEADDELAY switch _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _SHORTPULSE NO. 2 switch _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ INWIDTH switch_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _NARRISE TIME dial _ _ _ _ _ _ _ _ _ _ _ 1 usecPOLARITY switch_ _ _ _ _ _ _ _ _ _ POSPULSE RATE dial_ _ _ _ _ _ _ _ _ _ _1 kcCOARSE ATTN knob_ _ _ _ _ _ _ _ _ _ _ 250 OHMS

77

78

Figure 56.

TM

5895-217-35-132

Figure 57.

79

(3) Accurately mark the pulse generatorSEPARATION dial for 3-, 5-, and8-usec pulse separations as comparedto marker generator.

(4) Check the oscilloscope horizontal timecalibration to be sure that it isaccurate.

b. Uhf Signal Generator Delay. The follow-ing procedures are necessary to determine theamount of uhf signal generator delay to thepulse output from the pulse generator.

(1) Disconnect cable No. 6 at switch S6(fig. 58), and reconnect it to TeeAdapter UG-274/U on the pulsegenerator. Disconnect cable No. 10from the uhf signal generator andcable No. 14 from switch S5; thenreconnect cable No. 14 to uhf signalgenerator OUTPUT receptacle.

(2) Operate the oscilloscope, the pulsegenerator, the uhf signal generator,and the marker generator as in-structed in a above (1 USEC markersnot required).

(3) Calibrate the uhf signal generator at1,030 mc as described in its instruc-tion manual, and then adjust for 50percent external modulation from thepulse generator. Use the 0 dbmsetting.

(4) When stable CHANNEL A andCHANNEL B traces have been estab-lished on the oscilloscope, measure thedifference in time between the leadingedges of the second pulse on eachtrace. This delay is the uhf signalgenerator delay and should be re-recorded on the front panel for futureuse.

c. Power Output Circuit Losses. The testsetup of figure 58 introduces power losses be-tween the receiver-transmitter and the powerbridge.

Caution: Power bridge controls must alwaysbe set to their correct positions according to thebolometer in use, to prevent damage to thebolometer. Do not apply rf power to the bolom-eter when the power bridge is not connectedand turned on. Keep test setup switch S5 inthe DET position when not measuring outputpower or when the power bridge is turned off.

(1) To prevent overload of the attenuator,substitute the lossy line for the co-axial attenuator (fig. 58) when codeselections involve testing with morethan four pulses in a reply train. Thecoaxial attenuator is to be usedfor receiver-sensitivity measurementsonly.

(2) Set test setup switch S5 (fig. 58) tothe PWR position; switches S4 andS6 may be in any position. Set thepcwer bridge controls as follows:

Power bridge control Position

BOLOMETER RESISTANCE _ _ _ _ _ _ _ _ _ _ _ _ 200 ohms.POWER RANGE _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 100 milliwatts.TEMPERATURE COEFFICIENT_ _ +BIAS CURRENT_ _ _ _ _ _ _ _ _ _ _ _ 11-40BOL. RES. (chassis rear) _ _ _ _ _ _ _ _ _ _ FIXED.POWER switch _ _ _ _ _ _ _ _ _ _ _ __ ON.

(3) Zero-set the power bridge; follow theprocedures given in its instructionmanual. (The power bridge should beturned on throughout the followingtests.)

(4) Connect the slotted line to the at-tenuator in place of cable No. 15.Connect the other end of the slottedline to the uhf signal generator OUT-PUT. Interconnect the slotted lineand the standing wave meter.

(5) Set the uhf signal generator frequencyto 1,090-mc, 0-dbm output, and 1,000-cps modulation. Locate the points ofminimum voltage standing wave ratioand 1.5 to 1 by tuning both sectionsof the coaxial tuner. Mark these twopoints for future use in final testing.Lock the coaxial tuner in the mini-mum voltage standing wave ratioposition. Restore the original cableconnections shown in figure 58.

(6) Turn on the receiver-transmitter andthe pulse generator; set the controlunit master control to NORM, andthe function control to NORMAL.Interrogate the receiver-transmitteron 1,030 mc with a mode 1 signal(3-usec separation) and 0-dbm at-

80 AGO 10004A

(7)

(8)

57. Test

tenuator setting. Measure the averagepower output in milliwatts with powerbridge and record (wavemeter tunedto 1,000 mc).Disconnect the bolometer from the co-axial tuner and connect the bolometerto the directional coupler in place ofcable No. 13. Measure the averagepower output in milliwatts with thepower bridge.Subtract the reading obtained in (7)above from the reading obtained in(6) above; the difference is the poweroutput circuit loss. Record this figurefor future use.

Setup OperationThe test setup has four basic control con-

figurations which are used throughout chap-ters 3, 4, and 5. These four configurations willprovide equipment operation for most of thesectionalizing and localizing procedures.

Caution: To prevent overload of the attenu-ator, substitute the lossy line in place of theattenuator (fig. 58) when code selections in-volve testing with more than four pulses in areply train. Use the coaxial attenuator forreceiver-sensitivity measurements only.

a. Test Equipment. The oscilloscope and themarker generator are adjusted according to thetime elements required for the test. The powerbridge settings are given in paragraph 56c andthe POWER RANGE control is set to the scalerequired for substantial readings. The uhfsignal generator and pulse generator settingsare most commonly used are given below.

(1) Calibrate the uhf signal generator andrecord its dial settings for 1,030 mc;use a high quality frequency stand-ard, the wavemeter, or the internalcrystal oscillator. Set the remainingcontrols as follows:

Uhf signal generator control Position

Modulation control _ _ _ _ _ _ EXT. MODPULSE control _ _ _ _ _ _ _ _ _ +MOD. LEVEL control _ _ _ Adjust to obtain a 50 percent

reading on the PERCENTMODULATION meter.

AGO 10004A

(2) Calibrate the pulse generator as in-structed in paragraph 56. Set the con-trols as given below for tests; theSEPARATION, FINE ATTN, andDELAY (variable) controls are setaccording to test requirements. ThePULSE RATE dial is normally set to.5 kc, but when high accuracy timemeasurements are made with markergenerator, use 1 kc and set the SYNCselector knob to EXT GOING +.

Pulse generator control Position

SYNC switch _ _ _ _ _ _ _ _ _SYNC selector knob _ _ _ _ _

PULSE NO. 2 switch _ _ _ WIDTH control _ _ _ _ _ _ _ _ RISE TIME control _ _ _ COARSE ATTN_ _ _ _ _ _ _

LEADINT B (except for high ac-

curacy measurements asabove ).

IN1 usec.1 usecMULTIPLIER 1, OHMS 250

b. Configuration No. 1. This configurationof the test setup switches will permit measure-ment of receiver-transmitter sensitivity, band-width, frequency, suppression characteristics,power output and decoder troubleshooting, andtest requirements. Connect the oscilloscopeprobe to CHANNEL B for troubleshootingwaveform checks.

Test setup switch Position

S4 SUPERS5 PWRS6 MARK

c. Configuration No. 2. Use this test setupconfiguration for receiver-transmitter delay,range jitter, pulse reply, special reply pulse,code number assignment, interrogation rate,and random triggering rate tests. Connect theoscilloscope probe in CHANNEL A or CHAN-NEL B for troubleshooting waveform checks.

Test setup switch Position

S4 MARKS5 DETS6 DET

81

d. Configuration No. 3. This configurationprovides a quick sectionalizing check and over-all performance measurement. The oscilloscopemay be used with its probe connected to eitherchannel for signal tracing.

Test setup switch Position

S4 SUPERS5 PWRS6 VIDEO

e. Configuration No. 4. Use this configura-tion in general operation where comparisonsare desired between oscilloscope probe measure-ments and selected signals.

Test setup switch Position

S4 DETS5 DETS6 VIDEO

I

58. Localizing Troubleshooting Methods

a. Signal Tracing. Signal tracing is a methodby which the signal path is followed throughan equipment. It includes following the re-ceived signals, the signals initiated within theequipment because of the received signals, andthe resulting final output. In the receiver-transmitter, most of the signal tracing requireswaveform analysis on an oscilloscope (b be-low). Each step of the troubleshooting chartin paragraph 59 lists references to applicabletest points and waveforms. The following para-graphs will assist maintenance personnel induplicating the conditions for obtaining theproper waveforms.

b. Oscilloscope Procedures. Oscilloscope AN/USM-81 is used for observing the waveforms.Refer to TM 11-6625-219-12 for the operationof the oscilloscope. Use the probe furnishedwith the oscilloscope to check the test points.The probe in CHANNEL B, with test setupswitch S6 in the MARK position, permits com-parison of the waveforms to selected markersfrom the marker generator. Adjustment ofhorizontal sweep speeds depends on the pulsewidth, the number of pulses, and the type of

waveform to be observed. The pulse generatorDELAY and oscilloscope DELAY-TIMEMULTIPLIER controls are used to positionthe displays for proper timing measurements.Be sure to consider the attenuation factors andthe time delays of the probes and coaxial cablesused.

c. Waveforms. The normal waveforms thatshould be observed are illustrated with theschematic diagram of each subassembly. Thesewaveforms are designated by letters and de-scriptions, and the letters are keyed to circuitpoints on the schematic diagram to indicate thepoint at which the waveform was taken. Thetest equipment connections in figures 2 and 58provide several suitable setups for observingthe waveforms. Under each waveform is theoscilloscope horizontal sweep time and thevertical voltage calibration required for obtain-ing the waveform. The width, rise, decay, andseparation times, and the amplitude are indi-cated directly by the waveforms themselves.Because amplitude is not as important as timeand waveshape, waveforms, for successivestages, that involve only amplitude changes,have been omitted in this manual. Any cor-rections or repairs made to correct time andwaveshape discrepancies will normally correctsmall amplitude deficiencies. Where double-trace waveforms are shown, the required cali-brations for each channel are also indicated.Thorough knowledge of the use of the oscillo-scope is necessary to obtain the maximuminformation from waveforms shown in figures122 through 129. Figures 59 through 69 illus-trate the physical location of waveformmeasurement points for each subassembly. Theletters on the test point location illustrationsare consistent with the waveform letter des-ignations on the applicable subassemblyschematic diagram. Refer to the followingchart for coordinating the test point locationdiagrams to the appropriate schematic dia-gram.

Subassembly

IF-suppressor subchassis_ _ _ _Video amplifier card_ _ _ _ _ _ _ _ Decoder card _ _ _ _ _ _ _ _ _ _ _ Gate generator card _ _ _ _ _ _ _ _ _ _

Test pointlocationFig. No.

5960

61 and 6263

Schematic andwaveform dia-gram Fig. No.

123124125126

AGO 10004A82

Subassembly

Blocking oscillator and ringaround card.

Mode reply selector card _ _ _ _ _Ringing oscillator and coin-

cidence card.Modulator section _ _ _ _ _ _ _ _ _ _ _ Power supplies_ _ _ _ _ _ _ _ _ _ _ _ _

Test pointlocationFig. No.

64

6566

67 and 6869

Schematic andwaveform dia.gram Fig. No.

127

128129

122122

d. Voltage Measurements. Unless otherwisespecified, all voltage measurements are takenwith Multimeter AN/URM-105. Refer to TM11-6625-203-12 for the operation of the multi-meter. With the equipment operating and nosignal input to ANTENNA receptacle J101,measure the voltages at the points indicatedon the voltage and resistance diagram of theappropriate subassembly, and compare withthe values shown. Be sure to set the multimeterto the proper scale before connecting the leadsto the circuit. When measuring high voltages,turn off the transponder set, make the scalesetting, connect the test leads, and then turnon the equipment to prevent personal shockor shorts that could damage the equipment.

Caution: Momentarily shorting B+ andbias leads or connections to ground willusually damage one or more of the power sup-ply transistors.

e. Resistance Measurements. Resistancemeasurements are made with the multimeterwhen the transponder set is turned off. Itshould be observed in the voltage and resistancediagrams that certain resistance values areprefixed by a or sign. These resistancesare measured in circuits containing diodes andrequire the proper meter polarity connectionsto obtain the same results. This polarizationdoes not necessarily mean that the red or

positive lead is used for positive voltage read-ings. Multimeter AN/URM-105 has the nega-tive terminal of its internal battery connectedto the red lead during resistance measure-ments; therefore its black lead would be con-nected to the test point when a sign isindicated, and its red lead would be connectedto the test point when a sign is indicated.

59. Receiver-Transmitter Trouble Localization

a. General. The chart (b below) includes acomplete procedure for localizing troubleswithin the receiver-transmitter. This chartmay be used by third echelon personnel fortroubleshooting, because it includes a syste-matic procedure for tracing troubles to a de-fective subassembly (subchassis or printedcircuit card) or plug-in component. Thirdechelon maintenance personnel will replacethese components. Figure 70 illustrates theuse of the card removal tool fastened inside theright side cover. The chart may also be usedby fourth and fifth echelon maintenance per-sonnel to localize the trouble. The referencesthroughout this chart indicate the properisolating or additional troubleshooting pro-cedures to locate the defective part. The chartis based on signal tracing, using the oscilloscopeto check waveforms at key circuit test points(par. 58c). If this chart is used for thirdechelon maintenance, the equipment may beset up according to the procedures in paragraph9c. Disconnect the coder-decoder and check thewaveforms; use the oscilloscope probe con-nected to the oscilloscope CHANNEL B input,If this chart is used for fourth or fifth echelonmaintenance, set up the equipment accordingto the procedures in paragraph 55, calibrate thetest equipment as indicated in paragraph 56,and follow the test equipment operation pro-cedures in paragraph 57.

AGO 10004A 83

Figure 61.

TM5895-217-35-61 TM5895-217-35-63

TM5895-217-35-59

Figure 59. IF-suppressor subchassis, test point locations.

Figure 60. Video amplifier card, A. O. C. control andtest points location.

84

85

Figure 62.Figure 63.

TM5895-217-35-65TM5895-217-35-133

TM5895-217-35-67 TM5895-217-35-69

Figure 65.

Figure 64.

86

Figure 66.

87

TM5895-217-35-71

TM5895-217-35-134

88

Figure 68.

Figure 67.

TM5895-217-35-73

89

Figure 70.

TM5895-217-35-56

TM5895-217-35-76

Figure 69.

b.

90

fig. 6

para 72d fig. 55

fig. 93

par. 81

par. 72

fig 54

par. 77 par. 63

par. 78

par. 87

par. 86 fig. 54

par. 78

fig. 106

fig. 105 par. 64 par. 64

fig. 106

figure 122

figure 69

figure 123

figure 59

figure 124

figure 59

figure 124

figure 60

figure 124

figure 60

91

par. 64 fig. 106

par. 65 fig. 106

par. 65

fig. 106

par. 66

par. 68

par. 65 par. 66

par. 68

par. 70

par. 68

figure 125

figure 62

figure 126

figure 63

figure 128

figure 65

figure 65 figure 128 figure 128

figure 65

92

par. 67 par. 67

par. 70

fig. 105 fig. 92 par. 69

par. 71 par. 79d

par. 71

fig. 116 par. 71

figure 127

figure 64

figure 122

figure 68

figure 122

figure 67

figure 122 fig. 105

figure 122

fig. 58

Section IV. RECEIVER TRANSMITTER TROUBLE ISOLATION

60. Isolation Procedures

Data in the following paragraphs coordinatethe information in sections II and III to assistfourth and fifth echelon maintenance personnelin isolating a fault to a particular part. Thecharts in this section cover a card, a sub-chassis, or an operating section of the receiver-transmitter. Each paragraph also contains ad-ditional troubleshooting information in theform of transformer and inductor resistances,voltage and resistance data, and references toparts location and printed wiring illustrations.Reference is also made to test point locationdiagrams and schematic diagrams for each cardor subchassis. The card receptacle voltage andresistance diagrams (figs. 71 and 72) will alsoaid in troubleshooting the printed circuit cards.

61. Test Equipment Required

All the test equipment referred to in thefollowing charts are listed in paragraph 49.The troubleshooting bench test setup (fig. 58)is to be used for equipment operation. Followthe procedures in paragraphs 55 through 57for applying the proper input signals to thereceiver-transmitter. Waveforms and voltagesmust be taken with all subassemblies installed.

c. Converter Troubleshooting Chart.

Caution: To prevent overload of the attenu.ator, substitute the lossy line (par. 55a) inplace of the attenuator (fig. 58) whenever codeselections consist of more than four pulses in areply train. The attenuator is to be used forreceiver-sensitivity measurements only.

62. Converter Subchassis Troubleshooting

a. General. The chart (c below) containsinformation which aids converter trouble iso-lation. After completion of the checks and anyrepairs, realine the converter (par. 87). Referto schematic (figs. 10 and 122) and wiringdiagrams (fig. 117) for circuit connections,After the trouble is isolated, refer to paragraph77 for the repair procedures.

b. Converter Voltage and Resistance Meas-urements. Voltage and resistance measure-ments shown in figure 73 for tube V101 aretaken with Electronic Multimeter TS-505/Uand tube socket adapter. Make sure all coverplates are in place on the converter subchassisand no signal is applied to the input whenmeasurements are taken. Keep vtvm leads asshort as possible to avoid introducing straysignals and reactance to the oscillator circuit.

Item

1

2

Indication

Signals will not pass through con-verter.

Receiver weak, if.-suppressor sensi-tivity normal.

AGO 10004A

Probable trouble

Local oscillator section inoperative.

Mixer inoperative ---------------

Crystal Y101 off-frequency ------------

Converter misal ined - - - - - - - - - -

Procedure

Check tube V101 (fig. 55); replaceif defective.

Make voltage and resistance meas-urements or tube V101 (fig. 73).

Substitute crystal Y101 (figs. 98and 105).

Check alinement of oscillator andfrequency multipliers (par. 87).

Check diode CR101 (fig. 98); re-place if defective.

Check diode CR102 (fig. 98); re-place if defective.

Check capacitors C108 and C110;replace if defective.

Check alinement of preselector andharmonic selector cavities (par.87).

Check frequency or substitutecrystal (par. 87b).

Realine converter (par. 87).

93

94

Figure 71.

Tm

5895-217-35-72

95

Figure 72.

TM

5895-217-35-74

96

Figure 73.

TM

5895-217-35-57

97

Figure 74.

TM

5895-217-35-58

63. lF-Suppressor Subchassis Troubleshooting

a. General. The chart (c below) will permitmaintenance personnel to isolate IF-suppressorsubchassis troubles and perform correctivemaintenance. Refer to paragraph 86 for de-tailed alinement instructions when it is de-termined that all circuit parts are in serviceablecondition. Refer to the partial schematic dia-grams (figs. 12-17), overall schematic diagram(fig. 123), and wiring diagram (fig. 118) for

c. If-Suppressor Troubleshooting Chart.

circuit connections. After the trouble is iso-lated, refer to paragraph 78 for repair pro-cedures.

b. IF-Suppressor Voltage and ResistanceMeasurements. Voltage and resistance meas-urements on the IF-suppressor subchassis aremade with the bottom cover removed or withtube adapters. The subchassis may be recon-nected and rotated to provide access to tubesocket pins after removal. Voltages and re-sistances are shown in figure 74.

Item

1

2

8

4

98

Indication Probable trouble Procedure

No output at DET test point, oroutput weak and distorted.

Strong signals distortedtest point (fig. 59).

at DET

No waveform (D, fig. 123) presentat SUPPR test point (fig. 59).

No waveform (F, fig. 123) presentat VIDEO OUT test point.

Defective if. stage ---------------

Defective A.O.C. circuit ---------

Defective successive detector cir-cuits.

[mproperly alined if. stages ------Defective first video amplifier and

cathode follower V207.

Defective suppressor circuit -----------

Defective second video amplifier andcathode follower.

Check tubes V201 through V206(fig. 54) replace all defectivetubes.

Make voltage and resistance meas-urements of V201 through V206stages (fig. 74).

Check if. alinement (par. 86).Check diode CR209 (fig. 103). Fol-

low the diode testing proceduresin paragraph 73d.

Make voltage and resistance checks(fig. 74) of V202, V203, and V204control grid (pin 1) circuits.

Troubleshoot A.O.C. section of videoamplifier card (par. 64).

Check tubes V204 through V206(fig. 54); replace all defectivetubes.

Check pickoff diodes CR201, CR202,and CR203 (fig. 103). Follow theprocedures in paragraph 73d.

Make voltage and resistance checksof V204, V205, and V206 stages(fig. 74).

Realign if. stages (par. S6).Check tube V207 (fig. 54); replace

if defective.Check diode CR205 (fig. 103) fol-

lowing the procedures in para-graph 73d.

Check for waveforms (B and C,fig. 123) at test points (B and C,fig. 59) .

Make voltage and resistance checksof V207 stage (fig. 74).

Check for waveform (E, fig. 123)at test point (E, fig. 59). If nowaveform is present, check diodesCR204, CR206, and CR207 (fig.103). Refer to paragraph 73d.

Check tube V208 (fig. 54); replaceif defective.

Make voltage and resistance checksof V208 stages (fig. 74).

AGO 10004A

99

Figure 75.

TM

5895-217-35-60

64. Video Amplifier Card Troubleshootinga. General. The chart (c below) lists troubles

and corrective maintenance procedures for thevideo amplifier card. The waveform test pointsin figure 60 correspond to the waveforms andwaveform data in figure 124. All measure-ments are made with receiver-transmittercompletely assembled unless otherwise specified.Use the bench test setup shown in figure 58.Refer to partial schematic diagrams (figs. 19-22), complete schematic diagram (fig. 124),

c. Video Amplifier Troubleshooting Chart.

Item

1

2

3

4

5

6

7

8

9

10

100

Indication

No output to decoder card ----------

No waveforms present at eithertest point A.

No channel B waveform present attest point A.

No waveform present at test pointB.

No waveform present at test pointC.

No waveform present at test pointD.

No blanking of spurious replypulses or A.O.C. operation.

No A.O.C. operation, video blankingis normal.

A.O.C. inoperative, no waveform ispresent at test point F.

A.O.C. inoperative, normal wave-form is present at test point F.

and parts location printed wiring diagram (fig.76) for circuit connections. After the troublehas been isolated, replace the defective part byfollowing the procedures in paragraph 76.

b. Video Amplifier Voltage and ResistanceMeasurements. Tube voltage and resistancemeasurements shown in figure 75 are takenwith no signal input to the transponder set.Card receptacle voltage and resistance measure-ments (fig. 71) are also useful for isolatingtroubles.

Probable trouble

Open filament circuit ------------Defective stage in video amplifier

card.

No video input from IF-suppressorsubchassis.

Defective delay line DL301 --------

Defective spike suppressor stage------

Defective inverter stage ---------

Defective blanked cathode followerstage.

Defective blanking amplifier andcathode follower stage.

Defective A.O.C. amplifier or recti-fier.

Defective A.O.C. amplifier stage---

Defective A.O.C. rectifier or controlcircuit.

A.O.C. control out of adjustment-

AGO 10004A

Procedure

Check filament circuit continuity.Check waveforms A, B, C, and D

(fig. 124) at test points (fig. 60).Refer to items 2 through 6.

Troubleshoot IF-suppressor sub-chassis (par. 63).

Check the wiring that connects pin3 of P201 to pin 7 of J301 (fig.122).

Replace DL301 (fig. 76).

Remove and check V301 (figs. 54and 76); replace if defective.

Make voltage and resistance checkof V301 stage (fig. 75).

Remove and check V302 (figs. 54and 76); replace if defective.

Make voltage and resistance checkof V302 stages (fig. 75).

Remove and check V302 (figs. 54and 76); replace if defective.

Make voltage and resistance checkof V302 stages (fig. 75).

Remove and check V303 (figs. 54and 76); replace if defective.

Make voltage and resistance checkof V303 stages (fig. 75).

Check waveform F (fig. 124) at thetest point (fig. 60). If no wave-form is present, refer to item 9;if waveform is present, refer toitem 10.

Remove and check V304 (figs. 54and 76); replace if defective.

Make voltage and resistance checkof V304 stage (fig. 75).

Check diodes CR301 and CR302(fig. 76) by following the proce-dures in paragraph 73d.

Replace Zener diode CR303.Perform A.O.C. adjustment (par.

90).

65. Decorder Card Troubleshooting

a. General. Troubleshooting the decodercard requires operation of the control unit inthe five categories and using all three interro-gation modes. The single pulse output of thedecoder distribution circuit (par. 29c) is themain trigger pulse for developing the replycode. Troubleshooting items listed in the chart(e below) are guides for trouble isolation.Refer to the schematic diagrams (figs. 24, 25,and 125) and parts location printed wiringdiagram (fig. 78) for circuit connections. Afterthe trouble has been isolated, replace the defec-tive part (par. 76).

b. Decoder Voltage and Resistance Measure-ments. Voltage and resistance measurements

are given in figure 77. A, figure 94 identifiestube lead connections on the card edge. Usethe multimeter to make card receptacle voltageand resistance measurements (fig. 71) for ad-ditional circuit checks. Be sure diodes areisolated from the circuit when checks are madewith the multimeter or Crystal Rectifier TestSet TS-268/U.

c. Decoder Waveforms. Decoder card wave-forms, taken at the test points (figs. 61 and62), are coordinated with the waveforms onthe schematic diagram (fig. 125). Refer toparagraph 58 for the procedures on takingwaveforms.

d. Decoder Delay Line Resistances. T h echart below contains the out-of-circuit dcresistance of delay line DL351 (fig. 106).

Figure 77. Decoder card, tube voltage and resistance diagram.

AGO 10004A

T M 5 8 9 5 - 2 1 7 - 3 5 - 6 2

101

Delay lineterminals

Delay lineResistance (ohms) terminals Resistance (ohms)

1 to 2 NC 1 to 6 2,5001 to 3 1,300 1 to 7 NC1 to 4 NC 1 to 8 NC1 to 5 2,000 1 to 9 NC

e . Decoder Troubleshoot ing Chart .

Item

1

2

3

4

5

Indication

No decoder output, all modes

Probable trouble

Open filament circuit

No decoder ouput from one mode,in all operational categories.

Decoder outputs to all mode gatemultivibrators are normal, butmain gate multivibrator is not

triggered in one or all modes.Decoding is normal for all but re-

peated replies (I/P and EMER).

Decoding is normal for all butmodulated-emergency replies.

No B+ or bias voltage

No signal input from video ampli-fier card.

Defective input circuit _ _ _ _ _ _ _ _ _ _ _ _ _

Input to the decoder is out of co-incidence.

Defective mode decoder stage_ _ _ _ _

Defective decoder output distribu-tion circuit.

Inoperative switching diodes _ _ _ _ _ _

Inoperative switching diodes_ _ _ _ _ _

Procedure

Check continuity of resistor R366and the filaments of tubes V351,V352, and V353; replace defec-tive resistor or tube.

Check voltage and resistances atcard receptacle J35 (fig. 71).

Check for video waveform (A, fig.125) at pin 3 of receptacle J351.I f no waveform is present,troubleshoot video amplifier card(par. 64) or check continuity be-tween pin 3 of J351 and pin 2 ofJ301 (fig. 106).

Check resistance of delay lineDL351 (d above).

Check waveforms (A, fig. 125) atthe appropriate decoder controland suppressor grids for coinci-dence. If the second pulse at thesuppressor grid does not coincidewith the first pulse at the controlgrid, replace delay line DL351(fig. 106).

Remove and check the suspectedtube (figs. 54 and 78); replacethe tube if defective.

Make voltage and resistance checkof inoperable tube circuit (fig.77).

Check diodes CR351, CR352, andCR353 (fig. 78). Refer to para-graph 73d.

Check diodes CR354, CR355, andCR356 (fig. 78). Refer to para-graph 73d.

Check diodes CR355 and CR356(par. 73d).

Check relay K3 (fig. 106) for oper-ation or continuity (fig. 93).

102 AGO 10004A

103

Figure 79.

TM

5895-217-35-64

66. Gate Generator Card Troubleshootinga. General. Gate generator card trouble-

shooting procedures are listed in the chart (dbelow). Because this card is composed of fouralmost identical multivibrators, troubles arecombined. Faults applicable to one multivibra-tor can occur to the other three. Refer to thepartial schematic diagrams (figs. 27 and 28),complete schematic diagram (fig. 126), andparts location printed wiring diagram (fig. 80)for circuit connections. When the trouble hasbeen isolated, refer to paragraph 76 for therepair procedures.

b. Gate Generator Voltage and Resistance

d. Gate Generator Troubleshooting Chart.

Item

1

2

3

Measurements. Voltages and resistances fortube lead connection points are shown in figure79. B, figure 94 identifies tube connections.The card receptacle voltage and resistancemeasurements (fig. 71) will also assist in iso-lating troubles.

c. Gate Generator Waveforms. The wave-form test points shown in figure 63 correspondto the waveforms and waveform data in figure126. In cases of unusual troubles, use thewaveforms as a continuity measurement or forsignal tracing. Be alert for spurious signalswhich may cause erratic operation. Refer toparagraph 58 for waveform procedures.

Indication

No main gate pulses _ _ _ _ _ _ _ _ _ _ _ _ _

No main gate pulses to video ampli-fier card only.

No mode 1, 2, or 3 gate pulse _ _ _ _ _

Probable trouble

Main gate multivibrator nottriggered.

Inoperative main gate multivibra-tor stage.

Inoperative main gate amplifier_ _ _ _

Applicable mode gateis not triggered.

Applicable mode gateis inoperative.

multivibrator

multivibrator

Procedure

Check for main gate trigger (C,fig. 125) at pin 15 of J351 (fig.105). If no trigger is present,troubleshoot decoder card. Iftrigger is present, check for con-tinuity between pin 15 of J351and pin 12 of J401 (fig. 105).

Remove and check tube V404 (fig.54); replace the tube if defective.

Make voltage and resistance checkof V404 stage (fig. 79).

Troubleshoot main gate amplifierin mode reply selector card (par.68).

When interrogating in the appro-priate mode, check for modetrigger (B, fig. 125) at pin 14(mode 1), pin 12 (mode 2), orpin 11 (mode 3) of J351. If thetrigger is not present, trouble-shoot the decoder card (par. 65).If the trigger is present, checkcontinuity between the modecheckpoint used and pin 1 (mode1), pin 4 (mode 2), or pin 9(mode 3) of J401 (fig. 126).

Remove and check tube V401, V402,or V403 (fig. 54); replace thetube if defective.

Make voltage and resistance checkof the inoperative multivibrator(fig. 79).

104 AGO 10004A

67. Blocking Oscillator and Ring Around CardTroubleshooting

a. General. Troubleshooting procedures forthe blocking oscillator and ring around cardare included in the chart (e below). Be sure toobserve the waveshape and pulse width of allwaveforms. Check the waveforms in all opera-tional categories to determine extent of fault.Refer to the partial schematic diagrams (figs.30-32), complete schematic diagram (fig. 127),and the parts location-printed wiring diagram(fig. 82) for circuit connections. When thetrouble has been isolated, replace the defectivepart (par. 76).b. Blocking Oscillator and Ring Around

Voltage and Resistance Measurements. Volt-age and resistance measurements are shown infigure 81. Figure 94 will aid in locating tubeconnections. Refer to figure 71 for card re-ceptacle voltage and resistance measurements.

c. Blocking Oscillator and Ring Around

Waveforms. Waveforms shown in figure 127are present at the points illustrated in figure64. Complete data are given in figure 127 forduplicating the waveform conditions. Thesewaveforms may also be used for signal tracingin the card. Refer to paragraph 58 for wave-form procedures.

d. Blocking Oscillator and Ring AroundTransformer Data. Resistance measurementsfor transformers T501 and T502 are given inthe chart below. These measurements are out-Of-circuit resistances measured with Multi-meter AN/URM-105.

Transformer Terminal Resistance (ohms)

T501 1 to 2 7.53 to 4 8.25

T502 1 to 2 123 to 4 13

e. Blocking Oscillator and Ring Around Card Troubleshooting Chart.

Item

1

2

Indication Probable trouble

No output trigger pulses to delayline.

No waveform at test point A

AGO 10004A

Open filament circuit on blockingoscillator and ring around card.

Inoperative stage on blocking oscil-lator and ring around card.

No input from main gate multi-vibrator.

Inoperative ring around gate multi-vibrator.

Pulse train input to gated amplifiermissing.

Procedure

Check filament continuity throughtubes V501, V502, V503, and re-sistor R519 (fig. 82). Replacetubes with open filament or R519if open.

Check waveforms A, B, C, and D(fig. 127) at test points A, B, C,and D (fig. 64), then proceedto the applicable item (2-4) forthe isolating procedure.

Check for main gate at pin 13 ofJ401 (fig. 106). If no gate ispresent, troubleshoot gate gener-ator card (par. 66). If gate ispresent, check continuity betweenpin 13 of J401 and pin 3 of J501;check diode CR501 and capacitorC501 (fig. 82).

Remove and check tube V503 (fig.54); replace the tube if defec-tive.

Check for the 1-usec pulse at pin4 of J621 (fig. 106). If the pulseis missing, troubleshoot mode 1code switching card (par. 70);check resistance of delay lineDL601 (fig. 92). If the pulse ispresent, check continuity betweenpin 4 of J621 and pin 8 of J501;check capacitor C505.

105

Item

3

4

5

6

7

Indication

No waveform present at test pointB.

No waveform present at test pointC or D.

No repeated I/P and EMER re-plies.

Reply trains repeated incorrectnumber of times in one category.

All reply trains incorrectly re-peated in I/P and EMER cate-gories.

Probable trouble

lated amplifier inoperative _ _ _ _ _

Defective

Defective

trigger amplifier stage _ _

blocking oscillator stage_

No trigger input togate multivibrator.

ring around

Ring aroundpulse width

gate multivibratorincorrect.

R524 not correctly adjusted _ _ _ _ _ _ _

68. Mode Reply Selector Card Troubleshooting

a. General. Troubleshooting data in thechart (d below) isolates troubles by stage to thepart. Be sure that correct inputs to this cardare available as coincidence-type circuits willnot function unless timing is reasonablyaccurate. Refer to the partial schematic dia-gram (fig. 37), the card schematic diagram(fig. 128), and the parts location and printedwiring diagram (fig. 84) for the mode replyselector circuits. When the trouble has beenisolated, replace the defective part (par. 76).

Procedure

Remove and check tube V502 (fig.54); replace tube if defective.

Make a voltage and resistancecheck of V501 circuit (fig. 81).

Remove and check tube V501 (fig.54); replace the tube if defective.

Make a voltage and resistancecheck of V501A, leads 1, 2, and4, (fig. 81).

Check tube V501.Make a voltage and resistance

check of V501B, pins 5, 7, and8 (fig. 81).

Check continuity of the primaryand secondary windings of trans-former T501.

Check for trigger pulse waveform(D, fig. 125) at pin 13 of J351(fig. 106). I f no tr igger i spresent, troubleshoot decodercard (par. 65). If trigger ispresent, check continuity betweenpin 13 of J351 and pin 15 ofJ501. Check capacitor C509 (fig.82).

Check resistance values of R511,R512, and R513 (fig. 82) withcard removed.

Check capacitors C509 and C510with card removed.

Check operation and continuity ofrelays K1 and K2 (fig. 93).

Refer to paragraph 94 for adjust-ment procedure.

b. Mode Reply Selector Card Voltage andResistance Measurements. Voltage and resist-ance measurements are given in figure 83. Usefigure 94 to identify tube leads and figures 49,50, 51, and 71 for further assistance in voltagedistribution problems.

c. Mode Reply Selector Card Waveforms.Waveforms shown in figure 128 are present atpoints shown in figure 65. Data given witheach waveform indicate characteristics andtest conditions. Refer to paragraph 58 forwaveform procedures.

106 AGO 10004A

107

Figure 81.

TM

5895-217-35-65

108

Figure 83.

TM

5895-217-35-68

d. Mode Reply Selector Card Troubleshooting Chart.

Item

1

2

3

Indication

All mode reply selectors inoperative

Individual mode reply selectorstage inoperative.

No main gate pulses to video ampli-fier card.

Probable trouble

Open filament circuit

No input power to modelector card.

reply se-

Reply train amplifier inoperative

One or both inputs to affected replyselector stage are missing.

Defective mode reply selector stage

Defective normal/emergency relay_Inoperative main gate amplifier_ _ _

Procedure

Check continuity V451 throughV454 filaments and resistorsR469 through R472 (fig. 84).Replace tubes with open fila-ments or open resistors.

Check power distribution circuits( f i g s . 4 9 - 5 1 ) .Remove and check V454 (fig. 54);

replace tube if defective.Check diode CR451 (fig. 84); follow

the procedures in paragraph 73d.Make voltage and resistance check

of V454 (fig. 83).Check applicable waveform A, B,

or C (fig. 128) at test point (fig.65). If the control grid gate ismissing, check mode gate circuitor troubleshoot gate generatorcard (par. 66). If the suppressorgrid pulses are missing, check theapplicable reply code switchingcard (par. 70).

Remove and check the inoperativestages tube V451, V452, or V453,(fig. 54); replace defective tubes.

Make voltage and resistance checkof the inoperative stage (fig. 83).

Check operation and continuity ofrelay K4 (figs. 106 and 93).

Remove and check tube V454 (fig.54); replace tube if defective.

Make voltage and resistance checkof V454 stage (fig. 83).

Check for main gate pulse inputfrom main gate multivibrator. Ifmissing, troubleshoot gate gener-ator card (par. 66), or check thecircuit between the gate genera-tor and mode reply selector cards.

69. Ringing Oscillator and Coincidence Card b. Ringing Oscillator and Coincidence Card

Troubleshooting

a. General. Consult the chart (d below) forappropriate trouble and use procedure to iso-late the faulty part. The ringing oscillator andcoincidence card circuits in partial schematicdiagrams (figs. 41-43), card schematic dia-gram (fig. 129), and parts location and printedwiring diagram (fig. 86) are useful for isolat-ing troubles. When the trouble is isolated,replace the defective part (par. 76).

AGO 10004A

Voltage(1)

(2)

and Resistance Measurements.Tube voltage and resistance measure-ments are given in figure 85. Cardreceptacle voltage and resistancemeasurements are included in figure72. Use the vtvm for ringing oscilla-tor voltage measurements.Out-of-circuit dc resistances for trans-former T551 in the following chartare measured with Multimeter AN/URM-105.

109

110

Figure 85.

TM

5895-217-35-70

Transformer T551 Resistancec. Ringing Oscillator and Coincidence Card

Waveforms. Waveforms referenced in the(ohms)terminal

chart (d below) are taken at test points shown1 to 2 3.7 in figure 66 and are coordinated with wave-3 to 4 1 meg forms shown in figure 129. Refer to para-

graph 58 for waveform procedures.

d. Ringing Oscillator and Coincidence Card Troubleshooting Chart.

Item Indication

1

2

3

4

56

7

8

No reply train output from card_ _ _

No waveform at test point A_ _ _ _ _

No waveform at test point B_ _ _ _ _ _

No waveform at test point C_ _ _ _ _ _

No waveform at test point D_ _ _ _No waveform at test point E_ _ _ _ _

No waveform at test point F_ _ _ _ _

No waveform at test point G_ _ _ _ _

Probable trouble

Open filament circuit_ _ _ _ _ _ _ _

Input power missing_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Inoperative stage on ringing oscil-lator and coincidence card.

No main gate input to driver_ _ _ _ _ _

Inoperative drive stage_ _ _ _ _ _ _ _ _ _ _

Inoperative ringing oscillator stage

No input to first clipper stage-----Inoperative first or second clipper

stage.

Inoperative differentiator stage_ _ _

No mode reply code input to V554_ _

Procedure

Check continuity through the fila-ments of V551 through V554 andresistor R569. Replace defectivetube or resistor.

Check B+, bias, or filament powerdistribution circuit (figs. 49-51).

Check waveforms A through L (fig.129) at the test points (fig. 66),then proceed to the applicableitem (2–13).

Check for waveform A at pin 14of J401. If waveform is not pre-sent, troubleshoot main gatemultivibrator on gate generatorcard (par. 66). If waveform ispresent, check continuity betweenpin 14 of J401 and pin 13 of J551(fig. 106); check capacitor C551(fig. 86).

Remove and check tube V551 (fig.54); replace the tube if defective.

Make a voltage and resistance checkat leads 5, 7, and 8 of tube V551(fig. 85).

Remove and check tube V551; re-place the tube if defective.

Make a voltage and resistance checkat leads 1, 2, and 4 of tube V551(fig. 85).

Replace resistor R554 (fig. 86).Remove and check tube V552 (fig.

54); replace the tube if defective.Make a voltage and resistance check

of V552 stages (fig. 85).Remove and check tube V553 (fig.

54); replace the tube if defective.Make a voltage and resistance check

at leads 5, 7, and 8 of tube V553(fig. 85).

Check for pulse reply code at pin14 of J451 (fig. 106). If no pulsesare present, troubleshoot modereply selector card (par. 68). Ifpulses are present, check for con-tinuity between pin 14 of J451and pin 1 of J551 (fig: 106);check capacitor C559 (fig. 86)

AGO 10004A 111

Item

9

10

11

12

13

Indication

No waveform H at suppressor gridof V554.

Control grid and suppressor gridwaveform (H, fig. 129) positivepulses not in coincidence.

No waveform at test point J_ _ _ _ _ _

No waveform at test point K_ _ _ _ _ _

No waveform at test point J_ _ _ _ _ _

Probable trouble

Defective coupling circuit_ _ _ _ _ _ _ _ _

Incorrect ringing oscillator fre-quency.

Defective delay line_ _ _ _ _ _ _ _ _ _ _ _ _ _Inoperative coin coincidence detector

stage.

No input to blocking oscillator_ _ _ _

Defective blocking oscillator stage_

Procedure

Replace capacitor C557 (fig. 86).

Adjust inductor L551 (par. 92).Check capacitor C553 and inductor

L551 (fig. 86).Replace DL601 (fig. 105).Check coincidence of input pulses

(item 10).Remove and check tube V554 (fig.

54); replace tube if defective.Make a voltage and resistance check

of V554 stage (fig. 85).Replace transformer T551 (fig.

86).Remove and check tube V553 (fig.

54); replace tube if defective.Make a voltage and resistance check

at leads 1, 2, and 4 of V553 (fig.85).

70. Mode Reply Code Switching Card Trouble- reply train. The attenuator is to be used forshooting- receiver sensitivity measurements only.

Troubleshooting mode reply code switching b. Modulator-Transmitter Voltage and Re-cards is limited to checking diodes (par. 73d) sistance Measurements.and resistances. In-circuit resistances, are (1) Voltage and resistance measurementsshown in figure 72. Observe multimeter bat- are provided in figure 73.tery polarity for all resistance measurements (2) Out-of-circuit dc resistance data forto correctly simulate values given. Multimeter transformers T151, T152, and T153AN/URM-105 has the positive battery termi-nal connected to the black (negative) test lead.Cards may be removed for further isolationand checking values obtained from schematicdiagrams (figs. 130–132). Figures 87, 88, and89 illustrate parts location and printed wiringcircuits on the three code switching cards.

71. Modulator-Transmitter Troubleshootinga. General Modulator-transmitter trouble-

shooting procedures are indicated in the chart(d below).

Warning: High voltages are present in thiscircuit. Take adequate precautions to preventelectrical shock.

Caution: To prevent overload of attenuator,substitute the lossy line (par. 55a) in place ofthe attenuator (fig. 58) when code selectionsinvolve testing with more than four pulses in a

are given in the chart below.

Transformer

T151

T152

T153

Terminal

1 to 23 to 45 to 61 to 23 to 41 to 23 to 4

Resistance (ohms)

2.752.63.258.593.71 meg

c. Modulator-Transmitter Waveforms. Wave-forms A through F of figure 122 are present atpoints shown in figures 67 and 68. Checkpulse characteristics during signal tracing todetect distortion and pulse width changescaused by circuit faults.

112 AGO 10004A

d. Modulator-Transmitter Troubleshooting Chart.

Item

1

2

3

4

Indication

No transmitted reply trains, anycode or category.

Defect modulator - transmitterstage.

Pulses of reply train incorrect char-acteristics.

Short range to transmitted replies.

72. Power Supply Troubleshootinga. General. The chart (e below)

Probable troubIe

Standby circuit inoperative_ _ _ _ _ _ _

No input to trigger amplifier andblocking ocsillator.

Defective stage_ _ _ _ _ _ _ _ _ _

Trigger amplifier and blocking os-cillator inoperative.

Driver stage inoperative_ _ _ _ _ _ _ _ _

Modulator stage inoperative_ _ _ _ _ _

Transmitting oscillator inoperative

Trigger amplifier and blocking oscil-lator defective.

Ringing oscillator and coincidencecard defective.

Transmitter off frequency_ _ _ _ _ _ _ _

Lower power output_ _ _ _ _ _ _ _ _ _ _ _ _

containsinformation to aid power supply trouble iso-lation.

AGO 10004A

Procedure

Resistor R151 (fig. 7) open.Check voltage distribution (figs. 49-

51).Check for reply train at grid pin

2 of tube V151 (A, fig. 122).Recheck ringing oscillator and coin-

cidence card (par. 69).Signal trace with waveforms C, D,

E, and cathode of V154 (figs. 67,68, and 122).

Check voltage and resistance oftube V151 (fig. 73).

Test or substitute tube V151 (fig.54 or 105).

Check diode CR151 (par. 73d).Check voltage and resistance of

tube V152 (fig. 73).Test or substitute tube V152 (figs.

54 or 105).Check diode CR152 (par. 73d).Check voltage and resistance of

tube V153 (fig. 73).Caution: Do not check plate volt-

age of tube V153.Test or substitute tube V153 (fig.

54 or 105).Check voltage and resistance at

cathode of V154 (fig. 73).Substitute tube V154 (fig. 54).Replace oscillator cavity (par. 79).Check duplexer (fig. 116) for con-

tinuity and shorts.Check voltage and resistance of

tube V151 (fig. 73).Check or substitute transformer

T151 (fig. 106).Adjust resistor R154 (par. 93).Recheck card (par. 69).

Realign transmitting oscillator cav-ity (par. 88).

Check or replace transformer T153(fig. 106).

Substitute tube V154 (figs. 54 and105).

Check resistor R162 (fig. 105).Check or replace duplexer (fig.

116).

b. Power Supply Voltage and ResistanceMeasurements.

(1) Voltage and resistance measurementsfor the low- and high-voltage power

113

114

Figure 91.

Figure 90.

TM5895-217-35-77

TM5895-217-35-75

(2)

Part

supplies are shown in figure 90. Thesemeasurements are made with Multi-meter AN/URM-105.Additional out-of-circuit resistancesfor inductors L151 and L152, blowerB1, and transformers T1 and T2 aregiven in the following chart. Theseresistances are measured with Multi-meter AN/URM-105.

T e r m i n a l sR e s i s t a n c e

( o h m s )

B 1

L 1 5 1

L 1 5 2

T 1

Location(fig. No.)

1 0 8

1 0 6

1 0 6

1 0 6

1 t o 4 1 2 5

1 t o 5 1 3 5

1 5

1 5

1 t o 2 l e s s t h a n 1

1 t o 3

1 t o 4

1 t o 5

6 t o 7

8 t o 9

1 0 t o 1 1

l e s s t h a n 1

l e s s t h a n 1

l e s s t h a n 1

3 . 7 5

4 . 6

3 . 5

e. Power Supply Troubleshooting Chart.

Item

1

2

3

6

Part

T2

Location(fig. No.)

106

Terminals

1 to 21 to 31 to 41 to 56 to 78 to 9

10 to 11

Resistance(ohms)

less than 1less than 1less than 1less than 1

5520

less than 1

c. Power Supply Waveforms. Power supplytest point locations for troubleshooting areshown in figure 69 and the waveforms areshown in figure 122. Refer to paragraph 58for waveform procedures.

d. Transistor Troubleshooting. Waveformsand voltage-resistance measurements willusually isolate defective transistors. UseTransistor Test Set TS-1100/U to test thetransistors. Figure 91 indicates lead colorcodes for identification purposes.

Indication Probable trouble

N o p o w e r s u p p l y o u t p u t ( + 1 , 2 0 0

v d c , + 6 0 0 v d c , + 3 0 0 v d c , + 1 2 5

v d c , - 1 5 0 v d c , 6 v a c o r 1 1 5 v a c )

a n d t u b e s d o n o t l i g h t .

N o o u t p u t f r o m h i g h - v o l t a g e s u p -

ply (+1,200 vdc, +600 vdc, +300

v d c , a n d 6 v a c t o t u b e V 1 5 4 m i s s -

i n g ) .

N o o u t p u t f r o m l o w - v o l t a g e s u p p l y

(+125 vdc, —150 vdc, and 115

v a c t o B 1 m i s s i n g ) .

No +1,200 or +600 vdc output -----

N o + 1 , 2 0 0 v d c o u t p u t _ _ _ _ _ _ _ _ _ _ _

N o + 6 0 0 v d c o u t p u t _ _ _ _ _ _ _ _

F u s e F 1 0 1 o p e n _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

R e l a y K 5 d e f e c t i v e - - - - - - - - - - - - - - -

I n d u c t o r L 1 o p e n - - - - - - - - - - - - - - - -

T r a n s f o r m e r T 2 p r i m a r y o p e n - - - -

Transistor Q3 or Q4 defective _ _ _ _ _ _ _

R e s i s t o r R 8 o r R 9 o p e n _ _ _ _ _ _ _ _

R e l a y K 7 c o n t a c t s s t u c k i n o p e n

p o s i t i o n .

T r a n s f o r m e r T 1 p r i m a r y d e f e c t i v e .

Transistor Q1 or Q2 defective _ _ _ _ _ _ _ _

Resistor R2 or R3 open _ _ _ _ _ _ _

R e l a y K 6 c o n t a c t s s t u c k i n o p e n

p o s i t i o n .

T r a n s f o r m e r T 2 h i g h - v o l t a g e s e c -

o n d a r y d e f e c t i v e .

R e c t i f i e r s t r i n g C R 1 3 t h r o u g h C R 2 C

d e f e c t i v e .

Capacitor C8 defective _ _ _ _ _ _ _ _

Capacitor C7 defective_ _ _ _ _ _ _ _ _ _

D e f e c t i v e r e c t i f i e r i n s t r i n g C R 2 1

t h r o u g h C R 2 4 .

Capacitor C6 defective - - - - - - - - - -

Procedure

C h e c k f u s e F 1 0 1 ( f i g . 6 ) .

C h e c k r e l a y K 5 ( f i g s . 9 3 a n d 1 0 6 ) .

C h e c k c o n t i n u i t y t h r o u g h L 1 ( f i g .

1 0 5 ) .

C h e c k r e s i s t a n c e o f t r a n s f o r m e r T 2

( b a b o v e ) .

C h e c k ( d a b o v e ) o r r e p l a c e t r a n s i s -

t o r Q 3 o r Q 4 ( f i g s . 5 5 a n d 1 0 6 ) .

C h e c k r e s i s t a n c e o f R 8 o r R 9 ( f i g .

1 0 7 ) .

C h e c k r e l a y K 7 ( f i g s . 9 3 a n d 1 0 6 ) .

C h e c k r e s i s t a n c e o f t r a n s f o r m e r T 1

( b a b o v e ) .

C h e c k ( d a b o v e ) o r r e p l a c e t r a n s i s -

t o r Q 1 o r Q 2 ( f i g s . 5 5 a n d 1 0 6 ) .

C h e c k r e s i s t a n c e o f R 2 o r R 3 ( f i g .

1 0 7 ) .

C h e c k r e l a y K 6 ( f i g s . 9 3 a n d 1 0 6 ) .

C h e c k r e s i s t a n c e o f t r a n s f o r m e r T 2

t e r m i n a l s 6 a n d 7 ( b a b o v e ) .

C h e c k r e c t i f i e r s C R 1 3 t h r o u g h C R 2 0

( p a r . 7 3 d ) .

C h e c k c a p a c i t o r C 8 ( f i g . 1 0 6 ) .

C h e c k c a p a c i t o r C 7 ( f i g . 1 0 6 ) .

C h e c k r e c t i f i e r s C R 2 1 t h r o u g h C R 2 4

( p a r . 7 3 d ) .

C h e c k c a p a c i t o r C 6 ( f i g . 1 0 6 ) .

AGO 10004A 115

TM5895-217-35-78

Figure 92.

116

Item

7

8

9

1 0

1 1

Indication

No +300 vdc output _ _ _ _ _ _ _ _ _ _ _ _ _

N o 6 v a c o u t p u t ( t u b e V 1 5 4 d o e s

n o t l i g h t ) .

No +125 vdc output _ _ _ _ _ _ _ _ _ _ _ _ _

No -150 vdc output _ _ _ _ _ _ _ _ _ _ _ _

N o 1 1 5 v a c o u t p u t . ( B l o w e r B 1

d o e s n o t o p e r a t e . )

Probable trouble Procedure

Transformer T2 defective _ _ _ _ _ _ _ _ _ _

D e f e c t i v e r e c t i f i e r i n b r i d g e C R 9 t o

C R 1 2 .

Capacitor C5 defective _ _ _ _ _ _ _ _ _ _ _

Resistor R13 defective _ _ _ _ _ _ _ _ _ _ _

Transformer T2 defective _ _ _ _ _ _ _ _

Transformer T1 defective _ _ _ _ _ _ _ _ _

D e f e c t i v e r e c t i f i e r i n b r i d g e C R 1

t h r o u g h C R 4 .

Capacitor C3 defective _ _ _ _ _ _ _ _ _ _

Transformer T1 defective _ _ _ _ _ _ _ _

D e f e c t i v e r e c t i f i e r i n b r i d g e C R 5

t h r o u g h C R 8 .

Capacitor C4 defective _ _ _ _ _ _ _ _ _ _ _

T r a n s f o r m e r T1 defective _ _ _ _ _ _ _ _ _

C h e c k t r a n s f o r m e r T 2 t e r m i n a l s 8

a n d 9 ( b a b o v e ) .

C h e c k r e c t i f i e r s C R 9 t o C R 1 2 ( p a r .

7 3 d ) .

C h e c k c a p a c i t o r C 5 ( f i g . 1 0 6 ) .

C h e c k r e s i s t o r R 1 3 ( f i g . 1 0 7 ) .

C h e c k t r a n s f o r m e r T 2 , t e r m i n a l s

1 0 a n d 1 1 ( b a b o v e ) .

C h e c k t r a n s f o r m e r T 1 , t e r m i n a l s

6 a n d 7 ( b a b o v e ) .

C h e c k r e c t i f i e r s C R 1 t h o r u g h C R 4

( p a r . 7 3 d ) .

C h e c k c a p a c i t o r C 3 ( f i g . 1 0 5 ) .

C h e c k t r a n s f o r m e r T 1 , t e r m i n a l s

8 a n d 9 ( b a b o v e ) .

C h e c k r e c t i f i e r s C R 5 t h r o u g h C R 8

( p a r . 7 3 d ) .

C h e c k c a p a c i t o r C 4 ( f i g . 1 0 5 ) .

C h e c k t r a n s f o r m e r T 1 , t e r m i n a l s

1 0 a n d 1 1 ( b a b o v e ) .

117

TM5895-217-35-80Figure 94.

Figure 93.

TM 5895-217-35-79

73. Additional Troubleshooting Data

a. Delay Line DL601 Resistance Measure-ments. Resistance measurements shown infigure 92 are taken with Multimeter AN/URM-105.

b. Relay Measurements. Figure 93 containsrelay continuity and coil resistance data forrelays K1 through K7, K901, and K902. Tocheck energized contact continuity, disconnectthe relay coil terminals from chassis wiringand apply 27.5 volts dc to the applicable termi-nals. Resistances and continuity are measuredwith Multimeter AN/URM-105.

c. Subminiature Tube Connections. Figure94 illustrates colors of insulated tubing usedon the subminiature tubes, and also shows thearrangement of element leads. Further identi-fication assistance may be obtained from theappropriate card parts location and printedwiring diagram.

d. Diode Rectifier Data. The color code iden-tification system used for diodes in the receiver-transmitter is shown in figure 95. There aretwo test sets that can be used for testing dioderectifiers, Crystal Rectifier Test Set TS-268/Uor Multimeter AN/URM-105. Either of thesetest sets will give a relative indication of diodecondition. If the trouble indicates that a diodeis defective, replace the diode. Zener-typediodes must be replaced when suspected ofcausing faults. The chart below lists resistance,resistance ratio, and back current values foruse with either test set. Measure forward andback resistances on either test set; back cur-rents are measurable on diode tester only.Forward resistances listed are maximum re-sistance permissible, and back resistances aredetermined by resistance ratio and the meas-ured forward resistance. In some instances,the back resistance will exceed the maximum

TM5895-217-35-81

118

Figure 95.

Figure 96.

TM 5895-215-35-120

e. Mode 2 Switch. Test Points. Terminalboard TB101 (fig. 96) is on the right side ofthe receiver-transmitter behind the frontcover. This terminal board contains 14 testpoints for checking the mode 2 toggle switchcircuits. Test points 1 through 12 are forswitches 1 through 12. When one of theseswitches is turned on, continuity may. bemeasured between the switch test point andthe common (C) test point. The C test pointis connected to ground (test point G) for modi-fied or civil replies through contacts of relayK1.

CHAPTER 4

REPAIR AND ALINEMENT INSTRUCTIONS

Section I.

74. Generala. Common repair procedures generally will

be applicable in making transponder repairs.However, some special precautions must be ob-served, and special procedures employed, whendealing with printed circuits, crystal diodes,and transistors.

b. Make a thorough visual inspection of thetransponder set component to be repaired. De-termine if work is to be done near crystaldiodes, transistors, or printed circuits and whatphysical approach to the repair is necessary.

c. Before removing a subassembly, or part,always tag the leads to be disconnected so thatproper reconnection may be made.

75. Solderinga. While general soldering techniques will

be applicable to the common types of circuitryin the transponder, some modification of thesetechniques is necessary.

b. Special rules for guidance in soldering onthis equipment are:

REPAIRS

(1)

(2)

(3)

Do not use a soldering gun becauseits temperature is not controlled.Heat is destructive to printed circuits,crystal diodes, and transistors. Usingan uncontrolled heat source on ornear these parts can damage them.(The gun also sets up strong magneticfields which may damage crystaldiodes or transistors.)To limit the heat, use a 40- to 50-wattsoldering iron.When soldering near crystal diodes,transistors, and printed circuits, keepthe body of the soldering iron awayfrom these parts.

c. Soldering on printed circuits, crystal

AGO 10004A

diodes, and transistors require special care.Follow these rules when making soldered con-nections on printed circuits, crystal diodes, andtransistors.

(1)(2)(3)

(4)

(5)

Use a 40- to 50-watt soldering iron.Use only rosin-core solder.Solder quickly, applying heat onlylong enough to make a proper joint.(Excessive heat will cause blisteringor peeling of printed circuits, and maydamage crystal diodes or transistors.)When soldering crystal diodes or tran-sistor leads, use a heat sink to pre-vent heat conduction along the leadinto the diode or transistor. To dissi-pate the heat, hold the lead with along-nosed pliers between the solder-ing point and the diode or transistorbody.Two methods for removing parts fromprinted circuit boards are recom-mended.

N o t e . B e f o r e r e m o v i n g p a r t s f r o m p r i n t e d

c i r c u i t b o a r d s , i t m a y b e n e c e s s a r y t o d i s -

a s s e m b l e t h e c a r d ( p a r . 7 6 ) .

(a)

(b)

Where lead lengths are sufficient,melt the joint, push the leadthrough the board, and clip off theflattened lead end. The lead maythen be removed from the board.

Caution: Do not attempt to pullthe flattened end through the board,as this will enlarge the mountinghole. Be careful to avoid puttingpressure on the circuit board whenusing diagonal cutters in closequarters; pressure may fracturethe board.Where lead lengths are insufficient,or when insulating tubing preventspushing the lead through the board,

119

clip the leads between the part andthe board. Melt the joint and pushthe lead stubs out with a scribe.

(6) To install a new part, push the leadthrough the proper mounting hole,and clip it to the correct length.Flatten the end with pliers so that thelead contacts the foil, and solder thejoint in accordance with instructionsin (1) through (4) above. Wheresolder has filled the mounting hole,it may be reopened by melting thejoint and pushing a steel scribethrough the hole.

76. Printed Circuit Card Repairs(fig. 97)

Caution: Most of the cards have crystaldiodes mounted on their printed circuit boards.Both crystal diodes and printed circuit boardsare easily damaged by heat. Be extremely care-ful when handling or replacing parts on theprinted circuit boards.

a. Disassembly.(1)

(2)

(3)

(4)

(5)

(6)

120

Two captive holddown screws, one ateach end of the card, hold the printedcircuit cards in their receptacles.Loosen these screws until they dis-engage the captive chassis nuts.Firmly grasp the card and pullstraight up. Do not twist or tilt.

Caution: Avoid handling or dam-aging the printed wiring on the ex-posed surface of the fiber circuitboard.Do not disassemble the card unlessabsolutely necessary. Four screwsthrough the metal shield plate of eachcard hold the shield plate and printedcircuit board together.A fifth screw mounts the filamentresistor on the metal shield plate.When disassembling the card, thisscrew must be removed first.After removing the four assemblyscrews, the shield plate can be re-moved from the printed circuit board.The three switching cards do not haveshield plates or holddown screws.They are held in place by the recepta-

(7)

(8)

cle tension and the white plasticguides on the chassis at each end ofthe card receptacle.Switching cards may be removed byusing the card puller furnished (fig.70). This puller is clip-mounted in-side the right side panel. Use thispuller for removing switching cardsto avoid handling exposed parts ofthe card.The two hooked ends of the puller en-

gage in matching holes at the top ofthe switching cards to form a handlefor card removal.

Caution: Do not twist or tilt cardsduring removal because this maydamage base pins or separators.

b. Repair Procedures. General repair pro-cedures discussed in paragraphs 74 and 75 willserve for card repairs, except as noted below.

(1)

(2)

(3)

The blocking oscillator and ringaround card contains two variableresistors one of which (R524) ismounted on the shield plate. Be care-ful when opening this card to avoidbreaking the leads.The printed circuit board is not re-pairable. Replace the complete printedcircuit boards that are broken or havedamaged conductor foils.To replace the subminiature tubesused on the cards:

(a)

(b)

(c)

(d)

(e)

Clip the tube leads close to theprinted circuit board.Hold the tube shield in place insidethe tube clips, to prevent it fromsliding out with the tube.Withdraw the tube from the clipsand the shield.Replacement tubes. are inserted intothe shield and pushed into place,while holding the shield to preventit from being pushed out of theclips. Be sure to orient tube basecorrectly before insertion.Resolder the tube leads.

(4) To replace the tube shields, disassem-ble the card. Slide the old shield outof the tube clip; pry open the tubeclip jaws with a pair of long-nosed

AGO 10004A

121

TM5895-217-35-82

Figure 97.

(5)

(6)

(7)

pliers, and slide the replacement shieldin place between the clip fingers.Retaining rings for holddown screwsfit into the groove near the screwhead.Press the open jaws of the retainingring into this groove.Techniques for replacing electricalparts are covered in paragraph 75c.To replace most parts, it will be neces-sary to disassemble the card.Printed circuit boards are coated withDow-Corning 991 sealing and in-sulating compound after assembly.This compound burns away whensoldering heat is applied. Immediatelyafter the repairs are completed, applya light coating of this or an equivalentcompound on the exposed connections.

77. Converter Repairs(figs. 98 and 99)

a. Removal.(1)

(2)

(3)

Three mounting screws secure theconverter subchassis to the mainchassis. Two are located on the leftside of the receiver-transmitter andone is on the bottom of the receiver-transmitter case.Disconnect the duplexer cable fromconverter jack J102. Disconnect theconverter output cable from IF-suppressor jack J201. Unsolder thethree wire leads from the converter.Remove the three mounting screwsand lift out the converter subchassisfrom the right side of the receiver-transmitter.

b. Disassembly and Reassembly.(1)

(2)

(3)

Two cover plates inclose the con-verter circuitry. The larger is held byfour small screws at the corners. Thesmaller, an L-shaped strip, covers thetube socket and is held by two screws.Remove both cover plates for con-verter repairs.The converter cavities are not repair-able except for replacement of- theantenna cable receptacle and the threecavity couplers.

(a) The antenna cable receptacle, withthe antenna coupler on its under-

122

(b)

(c)

(d)

side, is installed in preselectorcavity Z101 by four small screws.It must be set in the mounting holewith its coupling loop parallel withthe tuning slug and with thegrounded end of this loop towardthe threaded end of Z101 tuningslug.Preselector cavity Z102 containsone coupling plate, held in place bytwo screws. To replace this coupler,remove mixer diode CR102. Un-solder the lead from the couplerfeedthrough insulator. Remove thescrew and nut that fastens CR102holder in place. Remove the couplermounting screws. Hold the mixerdiode clip out of the way whilelifting out the coupler. Replace thecoupler with the loop parallel withthe tuning slug, and with the cou-pler feedthrough insulator towardthe ground tie-point of capacitorC110. Reconnect the lead from themixer diode clip to the coupler feed-through insulator, and replace thescrews.Harmonic generator cavity Z103contains two couplers. Both are setwith the feedthrough insulatorstoward the side in which the tuningslugs are located. The harmonicgenerator diode (CR101) is con-nected to the coupler nearest thisside.

Caution: See paragraph 75 be-fore unsoldering CR101.Replace both cover plates after theconverter repairs are completed.

c. Replacement.(1)

(2)

Place the converter subchassis in themain chassis from the right side ofthe receiver-transmitter. Replace thethree mounting screws.Connect the converter output cable toIF-suppressor jack J201. Connect theduplexer cable to converter jack J102.Resolder the three wire leads to theconverter.

AGO 10004A

TM 5895-217-35-83

Figure 98. converter, interior view, crystal side, parts location.

78. IF Suppressor Subchassis Repairs(figs. 100-103)

a. The IF suppressor subchassis is securedto the main chassis by two captive screws.They are located near the top of the left sideof the receiver-transmitter housing, and passthrough the main chassis into lugs on the sub-chassis bottom cover.

b. The power cable connector is held downby two screws.

c. The bottom cover is held in place by sixnuts. Removal of the nuts will free the bottomcover.

d. No special repair techniques are requiredfor the IF-suppressor subchassis.

e. In compact circuits using miniature com-ponents, special care is required because of theconfined work space and the fact that partsmust be protected from heat.

Caution: Give special attention to the in-structions in paragraph 75, because there arecrystal diodes in this subchassis.

AGO 10004A

79. Transmitter Cavity Repairs(fig. 104)

a. Tube Replacement.(1)

(2)

(3)

Tube V154, a type 3CX100AS, ishoused inside the transmitting cavity,with its cooling fins outside the openend of the cavity. It is held in placeby a spring-fitting sleeve inside thecavity.To replace tube V154, remove thereceiver-transmitter front cover,which is held in place by two captivescrews.Grasp the tub-cooling fins firmly andpull the tube straight out. It may bestarted with a twist, and a twistingmotion may help to withdraw thetube. Do not jerk or pull the tubefrom side to side, because this maybreak the tube.

b. Cavity Removal.(1) The cavity is flange-mounted through

123

TM5895-217-35-85

Figure 99.

TM5895-217-35-84

TM 5895-217-35-85

(2)

(3)

124

Figure 100. IF suppressor subchassis, bottom view, resistor location.

the receiver-transmitter front panel (4) Remove the mounting screws andby four screws. withdraw the cavity through theRemove tube V154 from the cavity be- front-panel cutout.fore removing the cavity.Disconnect the cavity output cable, c. Repairs.the two leads to the cavity terminal (1) The transmitter cavity is not repair-plate, and the lead to the cavity flange. able.

AGO 10004A

Figure 101. IF suppressor subchassis, bottom view, capacitor location.

Figure 102. IF suppressor subchassis, bottom view, coil and transformer locations.

(2)

(3)

(4)

Figure 103. IF suppressor subchassis, bottom view, crystal and connector locations.

Two minor items in the cavity as-sembly are replaceable. These are thecontact spring and the retaining ringon the tuning screw.The retaining ring istype and is replacedinto the tuning screwThe contact spring is

a split-washerby pressing itgroove.secured to the

movable end of the tuning screw as-sembly by a single screw.

AGO 10004A

d. Cavity Replacement.(1) Slide the cavity in position through

the front panel cutout and replacethe mounting screws.

(2) Reconnect the cavity output cable, thetwo leads to the cavity terminal plate,and the lead to the cavity flange.

80. Modulator Section Repairs(figs. 105-108)

a. The modulator section consists of trigger

125

Figure 104.

TM

5895-217-35-86

126

Figure 105.

127

TM

5895-217-35-87

Figure 106.

TM

5895-217-35-88

129

Figure 107.

TM

5895-217-35-131

Figure 108.

TM 5895-217-35-89

amplifier-blocking oscillator V151, driverV152, and modulator V153 (fig. 105). Theassociated circuit parts for these stages arealso illustrated in figures 106, 107, and 108.

b. The modulator tube socket is part of asmall printed circuit board. Do not attemptto repair this board.

c. No special repair procedures are required.

81. Power Supply Repairs(fig. 109).

The power supply contains five subassem-blies: the transformer subassembly, the ca-pacitor subassembly (C3 and C4), the rectifiersubassembly, the 600-volt rectifier board. sub-assembly, and the 1,200-volt rectifier boardsubassembly.

130

a. Transformer Subassembly, Removal andReplacement. The transformer bracket ismounted at the rear of the receiver-transmittercase by six screws, three outside the case andthree inside, accessible from the left side.Twenty wires connect to transformers T1 andT2.

(1)(2)

Disconnect and tag the wires.Remove the six mounting screws andwithdraw the transformer subassem-bly from the left side of the receiver-transmitter case.To replace the transformer sub-assembly, set the subassembly inplace from the left side of the receiver-transmitter. Replace the six mount-ing screws.

AGO 10004A

(4) Reconnect the 20 tagged wires totransformers T1 and T2.

b. Capacitor C3 and C4 Subassembly Re-moval and Replacement (fig. 105).

(1)

(2)(3)

(4)

(5)

The mounting bracket for this sub-assembly is secured to the receiver-transmitter case with four screws, alloutside the case.Disconnect the four capacitor leads.Remove the four mounting screws andwithdraw the subassembly from theright side.To replace the capacitor subassembly,set the subassembly in place from theright side of the receiver-transmitter.Replace the four mounting screws.Reconnect the four capacitor leads.

c. Rectifier Board Subassembly Removal andReplacement (A, fig. 109).

(1)

(2)

(3)

(4)

(5)

The rectifier board subassembly ismounted on a bracket near the rearof the receiver-transmitter case onthe right side. It is secured to thisbracket by three screws.Remove the five rearmost subassemblycards to make room for a screwdriverfor removing the mounting screws.If repairs can be made without dis-connecting leads to the rectifiers, donot disconnect these leads.Remove the three mounting screwsand take out the rectifier subassembly.To replace the rectifier board sub-assembly, set the subassembly in placeand replace the three mountingscrews.

d. 600-Volt Rectifier Board Subassembly Re-moval and Replacement (B, fig. 109).

(1)

(2)

(3)

This subassembly is located on theleft side of the receiver-transmittercase at the bottom and front. It isheld in place by two screws.Disconnect the three leads to the recti-fier board subassembly.Remove the mounting screws and liftout the rectifierinsulating sheetboard.

AGO 10004A

board. Remove theunder the rectifier

(4) To replace the rectifier board sub-assembly, set the rectifier board inplace with the insulating sheet underit. Replace the mounting screws.

(5) Reconnect the three leads to the recti-fier board.

e. 1,200-Volt Rectifier Board SubassemblyRemoval and Replacement (C, fig. 109).

(1)

(2)

(3)

(4)

(5)

(6)

(7)

This subassembly is located on theleft side of the receiver-transmittercase at the top and front. It is con-cealed by capacitor C7, which must beremoved to give access to the rectifierboard subassembly.Two screws hold capacitor C7 inplace and must be removed to freethe capacitor. The leads to C7 arelong enough to avoid the need fordisconnecting them.With C7 laid back out of the way,disconnect the three leads to the recti-fier board.Remove the two mounting screws andlift out the rectifier board. Removethe insulating sheet under the rectifierboard.To replace the rectifier board sub-assembly, set the rectifier board inplace with the insulating sheet underit. Replace the two mounting screws.Reconnect the three leads to the recti-fier board.Reinstall capacitor C7 with the twoholding screws.

f. Transistors. Transistors are removedindividually. They are held in place by a singlestud and nut. Each transistor has two leadsto be disconnected before removal (fig. 91).

82. Receiver-Transmitter Connectora. The receiver-transmitter connector is

located on the rear panel, near the bottom. Itis inaccessible on all four sides because of thepresence of other parts, and can be reached onlyby removing the bottom-rear half-wraparoundcover.

b. The connector can be reached by removingthe bottom-rear half-wraparound cover, formedfrom a single piece of sheet metal.

131

Figure 109.

TM 5895-217-35-90

c. All screws in the bottom must be removed,except the two that hold the white plastic guidefor the switching cards.

(1)

(2)

(3)

Begin by removing modulator tubeV153 (fig. 105).Remove the four screws that hold themodulator tube base.Remove the remaining screws in thebottom cover, except the switchingcard guide screws. Some of the screwsare engaged in captive nuts, while thenuts engaging the others are free.Be sure to take out all free nuts andwashers to prevent the possibility ofshorts after reassembly.

d. With the screws removed from the bot-tom and rear, as indicated, the cover can belifted off. The connector will be detached fromthe rear cover, and will be exposed when therear cover is removed. The large capacitor justabove the connector may be removed, if neces-sary.

83. Control Unit Repairsa. The control unit (fig. 4, TM 11-5895-

217-12) is housed in a wraparound cover thatcloses the top and sides. To remove this cover,remove the six roundhead screws around the

132

edges of the rear panel; remove the two flat-head screws on the front edge of the top, andthe three flathead screws on each side.

b. To remove either of the two relay mount-ing brackets, remove the four screws: two onthe rear panel and two on the bottom plate.In the case of K901, one of the rear-panelscrews is locked by a wire seal (to the mount-ing nut on J901) which must be clipped toremove this screw.

c. To remove receptacle J901, cut the safetywire on the large nut, and loosen the receptaclenut. Take out the screws in both relay brackets,and remove the receptacle nut and receptacle.Push back the insulated tubing and carefullyunsolder the wires. After installation of thereplacement receptacle, tighten the nut andsafety-wire with #20 brass wire.

d. No special repair procedures are required.Caution: The control unit contains one

crystal diode. Be careful when soldering nearthis diode because it is easily damaged by heat.

84. Antenna Repair(fig. 5, TM 11-5895-217-12)

Replacement of the antenna cable receptaclecenter contact is the only repair permitted on

AGO 10004A

on the antenna. To replace this contact, proceedas follows:

a. Remove the receptacle outer shell.b. Pull out the dielectric (insulator) bush-

ing.

Section II.85. Test Equipment Required for Alinement

a. Test Equipment. The test equipmentlisted below is used for both IF and converteralinement. The assigned common name andtechnical manual are also listed in the chart.The transmitter alinement requires the sametest equipment listed in paragraph 49.

Nomenclature

O s c i l l o s c o p e A N /

U S M - 8 1 .

S w e e p S i g n a l G e n -

e r a t o r , B o o n t o n ,

R a d i o C o r p . T y p e

2 4 0 A .

P o w e r S u p p l y P P -

1 1 0 4 A / G o r e q u i v -

a l e n t .

Technical manual

T M 1 1 - 6 6 2 5 -

2 1 9 - 1 2 .

T M 1 1 - 5 1 2 6

Common name

O s c i l l o s c o p e .

S w e e p g e n e r a t o r .

2 8 - v o l t p o w e r

s o u r c e .

— — — —

b. Additional Equipment Required. Addi-tional equipment required for alinement islisted below with the assigned common name.

Description

I n t e r c o n n e c t c a b l e , c o n t r o l u n i t t o

r e c e i v e r - t r a n s m i t t e r .

1 1 5 - v o l t , 6 0 - c p s p o w e r s o u r c e .

C o a x i a l c a b l e , 4 f t R G - 6 2 / U w i t h a

U G - 8 8 / U c o n n e c t o r a t o n e e n d

a n d c l i p s a t t h e o t h e r e n d .

C o a x i a l c a b l e , 4 f t R G - 6 2 / U w i t h

u h f c o n n e c t o r a t o n e e n d o n l y .

C o a x i a l c a b l e , 4 f t R G - 6 2 / U w i t h

u h f c o n n e c t o r a t o n e e n d , U G -

8 8 / U c o n n e c t o r a t o t h e r e n d .

C o a x i a l c a b l e , 6 f t R G - 5 8 / U w i t h

U G - 8 8 / U c o n n e c t o r s a t o n e e n d

a n d D a g e C o r p . t y p e C B S N 3 4 7 8 -

1 c o n n e c t o r a t o t h e r e n d .

C o a x i a l c a b l e , 6 f t R G - 5 8 / U

U G 8 8 / U c o n n e c t o r s a t

e n d s .

O n e e a c h U G - 2 0 1 / U a d a p t e r .

AGO 10004A

w i t h

b o t h

Common name

B e n c h t e s t c a b l e

( p a r . 9 ) .

A c p o w e r s o u r c e .

C a b l e N o . 1 6 .

C a b l e N o . 1 7 .

C a b l e N o . 1 8 .

C a b l e N o . 1 9 .

C a b l e N o . 2 0 .

B N C t o N a d a p t e r .

c. Unscrew the center contact pin and re-place it with a serviceable contact pin.

d. Replace the dielectric bushing.

e. Replace the outer shell.

ALINEMENT

Description

O n e e a c h U G - 5 6 5 A / U a d a p t e r .

M i c r o a m m e t e r , 0 - 5 0 u a s h u n t e d b y

1 2 0 o h m s a n d f i l t e r e d b y 1 , 0 0 0

u u f ( f i g . 1 1 0 ) .

P l u g , S w i t c h c r a f t C o r p . t y p e 7 5 0

o r e q u i v a l e n t .

Common name

N to C adapter .

C o n v e r t e r c r y s t a l

c u r r e n t i n d i c a -

t o r .

C r y s t a l c u r r e n t

p l u g .

c. Sweep Generator Characteristics. TheBoonton Radio Corp. type 240A sweep genera-tor covers the frequency range from 4.5 to120 mc in five bands. The RF output is con-tinuously variable from 1 to 300,000 micro-volt, and the sweep rate is variable from 20 to70 cps with sweep widths to ±15 mc each sideof the center frequency. Crystal markersavailable at 2.5, 0.5, and 0.1 mc, and variablepip markers (two) are amplitude-adjustableand position-adjustable. Provisions are madefor internal calibration of the rf signal outputagainst the crystal oscillator.

d. Converter Crystal Current Indicator. The0-50 microammeter (fig. 110) used to alinethe converter subchassis is fabricated asfollows: use a 2-foot piece of shielded wire toconnect the shield to the shell and the centerwire to the tip of the Switchcraft Corp. type750 or equivalent plug. Place the 120-ohmresistor and the 1,000-micromicrofarads (µµf)capacitor across the meter terminals, and con-nect the shield to the positive meter terminal.Connect the center wire to the negative meterterminal. Do not insert this meter setup untilinstructed to do so by alinement instructions.

e. Test Setup. Fabricate the coaxial cableswith the connectors listed in paragraph 85b.Use figures 56 and 57 for coaxial connectorinstallation data.

86. IF Alinementa. Connect the equipment as shown in figure

110. Do not connect cable No. 20 because it

133

Figure 110.

134

TM

5895-217-35-91

is not used in the IF alinement. Turn on allthe test equipment and set the control unitmaster control to the STBY position.

Caution: Do not move the master control toany other position when the sweep generatoris in use. Adjust HI SENS control R225 on theIF suppressor subchassis (fig. 110) to its maxi-mum clockwise position, and calibrate thesweep generator at 60 mc; use its internalcrystal calibrator by following the proceduresin its instruction manual.

b. Set the oscilloscope controls as follows:

(1)

(2)

Set the sweep generator CRYSTALMARKER control to 2.5 mc and ad-just the sweep generator CRYSTALMARKER AMPLITUDE control toproduce visible markers.Adjust the sweep generator sweepWIDTH control so that the waveform(B, fig. 111) covers approximatelythree-fourths of the oscilloscope scale,and adjust the oscilloscope CHAN-NEL A VOLTS/CM for near full

AGO 10004A

(3)

(4)

(5)

scale display.control set toIncrease the

(Keep the VARIABLECALIBRATED.)sweep generator PIP

MARKER AMPLITUDE control untilmarkers are visible, and set the sweepgenerator PIP MARKER POSITIONcontrol No. 1 to the 2.5 mc markerwhich corresponds to the 60-mccenter-frequency.Set the sweep generator CRYSTALMARKER control to the .5 mc posi-tion; set pip marker No. 1 to 57 mcand pip marker No. 2 to 63 mc (eachis six 0.5 mc markers from 60 mc).Set the sweep generator CRYSTALMARKER control to OFF.

N o t e . D o n o t m a k e a n y a d j u s t m e n t s t o t h e

s w e e p g e n e r a t o r S W E E P W I D T H , S W E E P

R A T E , o r C E N T E R F R E Q c o n t r o l s a f t e r

c a l i b r a t i n g t h e p i p m a r k e r s .

e. When calibration has been completed,check the waveform against that shown in B,figure 111. If the waveform and markersagree, no IF alinement is necessary. If aline-ment is required, proceed as follows:

(1)

(2)

Aline IF transformers T202, T204,and T206 at 63 mc, and T203, T205,and T207 at 57 mc (A, fig. 111).This is accomplished by observing thepip markers and the correspondingwaveform humps, and adjusting eachtransformer so that a maximum humpamplitude is obtained at each pipmarker. Thus, when alinement iscompleted, the maximum hump ampli-tude points are 6 mc apart and equalin amplitude. Differences in ampli-tude greater than 10 percent indicatea defective stage or stages.Set the sweep generator output to100 microvolt and measure the out-put at the DET test point with theoscilloscope. Peak voltage shall be1.25 volts ±0.25 as measured on theoscilloscope, and the bandwidth shallnot be greater than 8 mc at the 3-dbpoints.

N o t e . T r a n s f o r m e r T 2 0 1 i s n o r m a l l y n o t

a d j u s t e d d u r i n g I F a l i n e m e n t b e c a u s e i t i s

u s e d t o c o r r e c t t h e f i n a l o v e r a l l c o n v e r t e r I F

w a v e f o r m .

135

Figure 111.

TM 5895-217-35-92

87. Converter Alinementa. Converter alinement is performed with

cables connected as shown in figure 110; exceptthat cable No. 19 is not used. The convertercrystal current indicator is inserted into re-ceptacle J202 only during oscillator and har-monic generator alinement. A harmonic out-put of the sweep generator is used for pre-selector cavity (Z101 and Z102) alinement.

b. Check crystal Y101 frequency to makesure that it is correct for the assigned receiverinput frequency.

Crystal frequency (mc) =Receiver frequency (mc) + 60 mc

12Turn on the transponder set and allow 10minutes warmup time for stabilization. Tuneinductors L101, L102, and cavity Z103 formaximum converter crystal current. Meterreadings between one-quarter and one half.scale are within operating limits. If the crystalfrequency must be checked because of off-frequency operation, use a standard frequencycounter having a 0.001 percent accuracy.

c. Converter preselectors Z101 and Z102 arealined by the use of the tenth harmonic of thesweep generator output.

(1) Set themc andthe 2.5

136

sweep generator dial to 102.5calibrate by zero-beating withmc-crystal marker.

(2)

(3)

When the 102.5-mc frequency hasbeen accurately located, set the sweepgenerator CRYSTAL MARKER con-trol to .5 mc and again note the102.5-mc zero beat.Move the center frequency dial to103-mc zero beat which is the first0.5-mc beat above 102.5 mc. If afrequency counter is available forfrequency measurement use it tocheck the 103-mc sweep generatorcenter frequency. (Type N410AWavemeter and type 612A Detectormay also be used to check the fre-quency.)

d. Alinement controls for the converter pre-selector are shown in A, figure 112. Becauseharmonic operation is used, multiply all crystalmarkers by 10; therefore, 2.5-mc markers willrepresent 25 mc on the oscilloscope display.

(1) Set the pip markers at 1,027 and 1,033mc and check Z101 and Z102 to de-termine at which frequency each hasbeen set. No fixed rule has beenadopted as to frequency assignmentfor these adjustments or for T201 inthe IF suppressor subchassis becausethey are adjusted for the best overallreceiver frequency response curve.

(2) Adjust Z101 and Z102 and check the

AGO 0004A

Figure 112.

TM 5895-217-35-93

(3)

(4)

pattern for symmetry as shown in B,figure 112. If one hump is appreci-ably higher than the other, readjustZ101and Z102 to opposite frequenciesfor possible improvement. The settingthat provides the best balance betweenthe two peaks should be the finalsetting.Adjust IF transformer T201 to placethe dip between peaks as near thecenter frequency as possible.Tighten each adjustment locknutwhile holding its adjustment screw.

88. Transmitting Oscillator Alinementa. Use the test setup of figure 58 and para-

graph 55 for transmitting oscillator alinement.Follow the test setup calibration proceduresin paragraph 56. Be sure that the coaxialtuner is properly tuned during the alinement.Set the test setup switches as follows: S4 toSUPPR, S5 to PWR, and S6 to VIDEO; andinterrogate the receiver-transmitter with amode 1 interrogation. Set the control unit as

AGO 10004A

follows: MODE 1 code control to position 73,function control to MOD, and master controlto NORM.

b. When the equipment has warmed up (ap-proximately 10 minutes), tune the wavemeteruntil a dip is seen in the power bridge indi-cation. The frequency shall be 1,090 mc ±1.If the frequency is not correct, aline the cavityas follows:

(1)

(2)

Loosen the tuning adjustment lockscrew (fig. 113) one-half turn andadjust the cavity tuning adjustmentin small increments, while checkingthe frequency with the wavemeter.Moving the tuning slide toward thefront of the receiver-transmitterraises the cavity resonant frequency.

Caution: Do not loosen the tuningadjustment lock screw too far at anytime because the retaining block (fig.104) will fall inside the cavity and willrequire disassembly of the cavity.Continue tuning until the properfrequency is obtained.

137

138

Figure 113.

TM

5895-217-35-94

(3) Tighten the tuning adjustment lock (3)screw and recheck the frequency.

c. After the frequency has been set, check (4)the transmitter power output as instructed inparagraph 104. To adjust peak power output, (5)the activity coupling probe (fig. 113) must beadjusted.

(1) Turn off the receiver-transmitter.(2) Disconnect coaxial connector P151,

and loosen the probe setscrews.

Screw the probe in to increase or outto decrease the power.Tighten the setscrews, reconnect P151,and recheck the power output.Repeat this adjustment as requiredto obtain 500-watt peak power output.

Note. Be sure that the wavemeter is de-tuned to 1,000 mc and that the coaxial tuneris correctly tuned when measuring outputpower.

Section III. ADJUSTMENTS

89. Test Equipment Required for AdjustmentsThe test equipment and materials used for

troubleshooting (par. 49) are also requiredfor making the receiver-transmitter adjust-ments. Follow the test setup procedures inparagraph 55; calibrate the test equipment byWing the procedures in paragraph 56.

90. A. O. C. AdjustmentUnless otherwise specified by military main-

tenance procedures, A.O.C. control R318 (fig.60) will be adjusted to begin regulation atinterrogation rates above 500 cps.

a. Set the control unit master control toNORM, and the function control to NORMAL,and interrogate the receiver-transmitter onmode 1.

b. Set test setup switch S4 to SUPPR, S5 toPWR, and S6 to VIDEO, and turn on all testequipment.

c. Set the pulse generator PULSE RATEcontrol set to .5 kc (500-cps interrogation rate).

d. Rotate control R318 to the full counter-clockwise position.

e. Adjust the uhf signal generator outputfor 50 percent transmitter triggering. This isdetermined by observing the main gate pulseon the oscilloscope, with the oscilloscopehorizontal sweep speed at the interrogationrate. When the intensity of the horizontaltrace and the intensity of the main gate pulseare equal, the transmitter is triggered by 50percent of the interrogations.

f. Increase the uhf signal generator output3 dmb; this should produce a full triggeringdisplay on CHANNEL B of the oscilloscope.

AGO 10004A

(Full triggering is the condition where nohorizontal trace appears in the pulse area.)

g. Set A. O. C. control R318 to produce 100percent firing (the point at which a horizontaltrace appears in the pulse area occasionally,but not more than once per second). Thisprocedure remains the same for all interroga-tion rates at which regulation is desired.

h. Turn off all equipment when the adjust-ment is completed.

91. Encoder Blocking Oscillator AdjustmentEncoder blocking oscillator control R523

(fig. 64) is adjusted to obtain the l-µsec outputpulses that are applied to delay line DL601.

a. Disconnect cable No. 7 (fig. 58) and con-nect the probe cable to CHANNEL B of theoscilloscope.

b. Connect this probe to test point D (fig.64) and set switch S5 to PWR and S6 toMARK.

c. Set the control unit master switch toNORM and the function control to NORMAL.

d. Turn on all test equipment. Adjust theoscilloscope to obtain waveform amplitude andcalibration of D, figure 127. Compare the widthof these waveforms with the 1-usec markersfrom the marker generator.

e. Adjust the pulse width to 1 usec ±0.1with control R523 (fig. 64) in blocking oscilla-tor and ring around card.

f. When the adjustment is completed, turnoff all test equipment and reconnect cableNo. 7 to CHANNEL B of the oscilloscope.

92. Ringing Oscillator AdjustmentThe ringing oscillator is adjusted to provide

139

the accurate 1.45-usec spacing for the replypulses.

a. Disconnect cable No. 7 (fig. 58) from theoscilloscope CHANNEL B, and connect theoscilloscope probe to CHANNEL B. Connectthe probe to test point H of figure 66 (sup-pressor grid of tuber V554).

b. Set test setup switch S5 to PWR and S6to MARK, and turn on all test equipment.

c. Set the control unit master control toNORM and the function control to NORMAL

d. Adjust the oscilloscope horizontal sweepto .1 usec, DELAYING SWEEP; and the pulsegenerator to obtain a mode 1 interrogation(3-usec pulse spacing).

e. Adjust the amplitudes and positions ofthe two traces on the oscilloscope for easycomparison.

f. Check and adjust the ringing oscillator asfollows:

(1)

(2)

(3)

(4)

(5)

140

Rotate the oscilloscope DELAY-TIMEMULTIPLIER control to move thewaveforms to the right until the firstcomplete cycle of the ringing oscillatoris visible.Aline the 50 percent amplitude pointof the leading edge on a positive goingpeak of the ringing oscillator outputwith a vertical line on the scale, andrecord the oscilloscope DELAY-TIMEMULTIPLIER dial reading. Thescale vertical line chosen for this stepwill be used as the reference line forall steps to follow.Continue rotating the oscilloscopeDELAY-TIME MULTIPLIER controlto bring the leading edge 50 percentamplitude point of the closest 1-usecmarker pulse to the reference line.Record the oscilloscope DELAY-TIME MULTIPLIER dial reading.Slowly rotate the oscilloscope DELAY-TIME MULTIPLIER control to movewaveforms to the left, and count 60complete ringing oscillator cycles asthe 50 percent leading edge pointspass the reference line. Record theoscilloscope DELAY-TIME MULTI-PLIER reading.Return to the reference point ((3)

(6)

above) and count eighty-seven 1-usecmarker pulses at the reference line.Record the oscilloscope DELAY-TIME MULTIPLIER dial reading.Adjust inductor L551 (fig. 66) untilthe difference in oscilloscope DELAY-TIME MULTIPLIER dial readingsfor the ringing oscillator in (2) and(4) above equals the difference inoscilloscope DELAY-TIME MULTI-PLIER dial readings for the markerpulses in (3) and (5) above. Whenthis occurs, 60 complete ringing oscil-lator cycles will be enclosed by 87marker pulses. The period of onecomplete ringing oscillator cycle mustbe 1.45 usec ±0.05. When this occurs,the adjustment is completed.

g. Turn off all equipment and reconnectcable No. 7 to CHANNEL B of the oscilloscope.

93. Blocking Oscillator AdjustmentThe blocking oscillator is adjusted to obtain

the 0.45usec pulse width for the transmittedpulses.

a. Connect the receiver-transmitter and thetest equipment as shown in figure 58 withswitch S4 in the DET position, S5 in the DETposition, and S6 in the MARK position.

b. Set all 12 mode 2 selector switches to ON,and set the control unit as follows: mode 2switch to ON, master control to NORM, andfunction control to MOD.

c. Turn on all test equipment, select 1-usecmarkers from the marker generator, and inter-rogate the receiver-transmitter with mode 2(5-usec spaced pulses). A full mode 2 replytrain should appear on CHANNEL B trackwith horizontal sweep set for 5 usec/cm.

d. Set the horizontal sweep controls for 0.1usec/cm (MAIN SWEEP DELAYED) andadjust control R154 (fig. 67) for a pulse widthof 0.45 usec ±0.1.

e. Rotate the oscilloscope DELAY-TIMEMULTIPLIER control to view each pulse ofthe replay train; none of the pulses must exceedthe limits of 0.35 to 0.55-usec pulse width.Adjust control R154 to place all pulses in thereply train within the limits.

AGO 10004A

94. Ring Around Gate Multivibrator Adjustmenta. With the equipment setup as in figure 58,

disconnect cable No. 7 from the oscilloscope andconnect the probe cable to CHANNEL B input.Connect the probe to test point H (fig. 64) andturn on all test equipment. Set test setupswitch S5 to PWR and S6 to MARK.

b. Following are the procedures for check-ing each of the three ring around gate multi-vibrator

(1)

(2)

(3)

pulse widths. Set the control unit master control toEMER and the function control toNORMAL; measure the width of thepulse on the oscilloscope channel Btrace with a mode 1 (3-usec spacedpulses) interrogation. The pulseshould be approximately 57 usec wide.With the control unit master controlin EMER, the function control in theMOD position, a mode 1 interrogation,and MODE 1 code control set to 73,measure the pulse width on the oscil-loscope channel B trace. The pulseshould be approximately 87 usec.Set the control unit master control toNORM and the function control toMOD. Interrogate the receiver-trans-mitter on mode 1 with the MODE 1code control set to 73. Measure thepulse width on the oscilloscope chan-nel B trace after the control unit I/Pswitch has been operated. The pulse

(4)should be approximately 37 usec wide.Adjust control R524 (fig. 64) to thepoint at which the three pulse widths(37, 57, and 87 usec) are as close tocorrect as possible.

95. Receiver Sensitivity AdjustmentWith the equipment set up as in figure 58,

turn on all test equipment and use the test setupconfiguration of paragraph 57a and c. Measurereceiver sensitivity at the transmitter 50 per-cent triggering point as follows:

a. Set the uhf signal generator to 1,030 mcand interrogate with 3-usec pulse separation.Set the control unit master control to NORM.Adjust the uhf signal generator output for 50percent transmitter triggering. This can bedetermined by observing the main gate pulseon the oscilloscope. With the oscilloscope hori-zontal sweep triggered at the interrogationrate; the intensity of the horizontal trace, andthe main gate pulse are equal when 50 percenttriggering occurs.

b. If the receiver-transmitter signal input isless than -76 dbm (36 microvolts), at theANTENNA receptacle, adjust R225 (fig. 59)to produce 50 percent triggering with a signalinput of -74 dbm (43 microvolts).

c. Place the control unit master control inthe LOW position, increase the signal input 30dbm, and adjust R226 (fig. 59) for 50 percenttriggering.

AGO 10004A 141

CHAPTER 5

FINAL TESTING

96. Purpose of Final TestingThe tests outlined in this chapter provide a

systematic procedure for measuring the per-formance capability of a repaired equipment.Equipment that meets the tolerances specifiedin these tests will furnish satisfactory opera-tion, equivalent to that of new equipment. Thecontrol unit may be tested when used with thereceiver-transmitter, or by performing the con-trol unit continuity checks in paragraph 52.There are no tests for the antenna.

97. Test Equipment Required for Final TestingThe same test equipment that was used for

troubleshooting (par. 49) is required for finaltesting. Refer to the appropriate technical orinstruction manual for the operating instruc-tions of each test equipment item. Use the testsetup pin figure 58 for all tests in this chapter.The instructions given with each test providethe best method for the test under considera-tion. To provide a complete check, perform thetests in the order of the following paragraphs.Prior to each test, check and adjust the inputpower at fuse F101 to exactly 27.5 volts dc.

98. Receiver Sensitivity TestThe receiver sensitivity tests (triggering

level) determine the minimum input signal re-quired to provide 50 percent triggering of thetransmitter. This is determined by observingthe main gate pulse on the oscilloscope withthe oscilloscope horizontal sweep speed at theinterrogation rate. When the intensities of themain gate pulse trace and baseline trace(interrogations that do not trigger the maingate multivibrator) are equal, the transmitteris producing reply trains for one-half of thereceived interrogations. Use the test setupoperating procedures described in paragraph57a and d.

Caution: Be sure that the power bridge isconnected and operating properly (par. 57c),

142

and that the code controls are set for minimumpulses in the reply train before turning on thereceiver-transmitter.

a. Adjust the uhf signal generator outputfrequency to 1,030 mc. Set the control unitmaster control to NORM.

b. Adjust the signal generator output leveluntil 50 percent triggering is observed on theoscilloscope.

c. Adjust the pulse generator pulse separa-tion for Mode 1 (3 usec), mode 2 (5 usec), andmode 3 (8 usec) interrogation, and note thesignal input required for 50 percent triggeringon each mode. This is the receiver sensitivity.

d. The receiver sensitivity must be -72 to-76 dbm (58 to 36 microvolt) for all threeinterrogation modes. Record the sensitivityvalues obtained for use in other parts of thefinal test.

99. Receiver Bandwidth TestThe following procedure (a through c below)

is used to measure the receiver bandwidth be-tween the 3-db and the 40-db points. The band-width shall be 6 to 8 mc between the two 3-dbpoints, and not greater than 29 mc between thetwo 40-db points. Use the test setup configura-tion described in paragraph 57a and c.

a. Set the uhf signal generator output levelto the required sensitivity value (par. 98d).

b. Increase the signal output 3 db, and rotatethe uhf signal generator frequency dial aboveand below 1,030 mc to locate the new 50 per-cent transmitter triggering points. The differ-ence between these two frequencies is the band-width at 3 db.

c. Increase the signal output 40 db above thevalue obtained in paragraph 98, and againdetermine the upper and lower 50 percenttransmitter triggering points. The differencebetween these two frequencies is the bandwidthat 40 db.

AGO 10004A

100. Receiver Center-Frequency Test

The receiver center-frequency may be com-puted from the half-power (3 db) frequenciesdetermined in paragraph 99. The center-fre-quency is the frequency midway between thetwo frequencies at the half-power points, andwill be 1,030 mc ±1.

101. Sensitivity Level Selection Test

Determine the receiver sensitivity (par. 98)with the control unit master control in theNORM position. Set the master control to theLOW position and recheck the receiver, sensi-tivity. The LOW sensitivity will be 30 dbmless than the NORM sensitivity.

102. Receiver Image Response Test

Using the test and sensitivity value obtainedin paragraph 98, set the uhf signal generatorto 1,150 mc and increase the signal output toestablish 50 percent triggering. Rock the uhfsignal generator frequency dial to find a maxi-mum signal point and again adjust the attenu-ator for 50 percent triggering. The sensitivitywill be at least 50 dbm below the sensitivityobtained in paragraph 98.

103. Main Gate Characteristic Test

Main gate pulse characteristics will be asfollows: the pulse width 120 usec + 30 -20,the peak amplitude not less than 20 volts orgreater than 70 volts, the rise time equal toor greater than 10 volts per usec, and the decaytime equal to or greater than 10 volts per usec.Use the test setup configuration described inparagraph 57a and b.

a. Use a 3-usec pulse separation (mode 1)interrogation, and trigger the pulse generatorat 1 kc with the marker generator. Set theuhf signal generator attenuator to apply -69dbm signal input to the ANTENNA receptacleof the receiver-transmitter.

b. Observe and measure the pulse waveformon CHANNEL B of the oscilloscope with itssweep speed set at the 20 usec/cm rate. Usethe marker generator outputs as required foraccurate timing of the waveform.

104. Transmitter Power Output Test

ator, substitute the lossy line (par. 55a) inplace of the attenuator (fig. 58) when codeselections involve testing with more than fourpulses in a reply train. Use the attenuator forreceiver-sensitivity measurements only.

Compute the transmitter output peak powerfrom the power bridge average power readingby the following formula:

W = Average pulse width in seconds.N = Number of pulses in reply train (4

used in test).PRR = Pulse repetition rate, or PULSE

RATE of pulse generator (500 usedin test).

The peak power output shall not be less than251 watts or greater than 1,000 watts with theminimum voltage standing wave ratio. Thepeak power must not be less than 158.5 wattswith a voltage standing wave radio of 1.5:1(3.5 db) .

a. Use the test setup configuration describedin paragraph 57a and b. Be sure that the powerbridge is operating, connected, and properlyadjusted before turning the transponder set on.

b. Adjust the pulse generator to provide 50percent modulation of the uhf signal generator1,030 mc output. Adjust the pulse generatorfor 3 usec separation (mode 1) pulses at aPULSE RATE .5 KC.

c. Increase the uhf signal generator attenu-ator to 0 DBM and set the control unit as fol-lows: the master control to NORM, the func-tion control to MOD, and the MODE 1 codeControl at the .03 position. Compute the peakpower; use the average power reading from thepower bridge. Record the average power andpeak power.

d. Repeat the procedure given in c abovewith the control unit set for EMER andNORM/IP and with 5 and 8 usec (mode 2 and3) pulse, separations. The peak power outputshall not vary more than 10 percent from thevalue obtained in c above.

Caution: To prevent overload of the attenu- e. Increase the PULSE RATE from 0.5 to

AGO 10004A 143

2.0 kc. The average power reading on thepower bridge shall not be more than 1 db belowthat obtained in c above.

f. Increase the PULSE RATE from 2.0 to3.5 kc. The average power reading on thepower bridge will not be more than 3 db belowthat obtained in c above.

g. Set the coaxial tuner to 1.5:1 voltagestanding wave ratio points calibrated in para-graph 56, and the PULSE RATE to .5 KC.Measure the average power and compute thepeak power output.

105. Transmitter Frequency Test

With the equipment operating as instructedin paragraph 104a, b, c, and d, tune the wave-meter for a minimum indication on the powerbridge. The frequency read on the wavemeterdial shall be 1,090 mc ±1.

Caution: To prevent overload of the attenu-ator, substitute the l0SSY line (par. 55a) inplace of the attenuator (fig. 58) when codeselections involve testing with more than fourpulses in a reply train. The attenuator is to beused for receiver-sensitivity measurementsonly.

106. Receiver-Transmitter Range Jitter TestOperate the equipment as instructed in para-

graph 57a and b for the range jitter test. Ob-serve the horizontal movement (jitter) of suc-cessive reply trains on oscilloscope channel Btrace. Range jitter shall not exceed 0.2 usec.Use approximately -30-dbm signal input atthe receiver-transmitter ANTENNA receptacleand several interrogation modes and reply codetrains.

107. Receiver-Transmitter Delay TestReceiver-transmitter delay time shall not

exceed 3 usec ±0.3 when interrogating pulsesare 3, 5, or 8 usec ±0.2 at signal inputs 6 to 50dbm above normal triggering level (par. 98).

Caution: To prevent overload of the attenu-ator, substitute the lossy line in place of theattenuator (fig. 58) when code selections in-volve testing with more than four pulses in areply train, The attenuator is to be used forreceiver-sensitivity measurements only.

144

a. Determine the uhf signal generator delayif it is not known (par. 56). Disconnect cableNo. 6 from test setup switch S6 (fig. 58) andreconnect it to the UG-274/U tee adapter onthe pulse generator OUTPUT receptacle.

b. With the equipment operating as in-structed in paragraph 57a and b, measure andrecord the time between the leading edge of thesecond pulse on the channel A trace and theleading edge of the first reply train pulse on thechannel B trace.

c. Compute the receiver-transmitter delay bysubtracting the uhf signal generator delay fromthe time obtained in b above.

108. Receiver-Transmitter Pulse Reply TestEach coded reply train from the receiver-

transmitter must have the characteristics listedin a below. Consult chapter 2 for the explana-tion of code number assignments if necessary.Examine each pulse and the spacing betweenpulses of a maximum pulse reply train in sev-eral operational categories. Check each of thepossible codes for the correct number assign-ment and the position of its pulses. Refer tofigure 5 for pulse positions.

Caution: To prevent overload of attenuator,substitute the lossy line (par. 55a) in place ofthe attenuator (fig. 58) when code selectionsinvolve testing with more than four pulses in areply train. The attenuator is to be used forreceiver-sensitivity measurements only.

a. The pulse characteristics are listed below;spacings between pulses and reply trains areas follows: mode 1 or 3 interrogation, pulseseparation 2.9 usec ±0.5; mode 2, 1.45 usec±.05; the spacing between repeated replytrains is 4.35 usec ±.1. I/P replies are dis-played for 30 seconds +20 -15.

Fig. 5

Fig. 5

Fig. 5

b. Check the function control NORMAL reply codes as listed below; use the test setup configura-tion (par. 57a and c). Except for pulse separation, all pulses are to have characteristics describedin a above.

c. Check the function control MOD reply codes as listed below; use the test setup configuration(par. 57a and c). All pulses have characteristics and separations described in a above.

d. Check the function control CIVIL reply codes (identical with the MOD position except forI/P replies). The CIVIL-I/P replies listed below have pulse characteristics and separations listedin a above. Use test setup configuration (par. 57a and c). For each check, place the I/P switchto the I/P position.

109. Single Interrogation Pulse Test to OUT and vary the pulse width and the

The receiver-transmitter will not transmit PULSE RATE controls through their ranges.

a reply for single-pulse interrogations having c. No transmitted replies should be presenta pulse width from 0.5 to 10 usec at pulse in the NORMAL, MOD, or CIVIL positions ofrepetition rates from 0.05 to 10 kc. the function control.

a. With the test setup configuration (par.57a and c), interrogate the receiver-transmitter 110. Second Interrogation Pulse Width Test

normally to check its response, and adjust the The width of the second pulse of a mode 1oscilloscope. interrogation shall not be narrower than the

b. Set pulse generator PULSE NO. 2 switch first pulse by more than 0.2 usec.

AGO 10004A 145

a. Use the test setup configuration (par. 57aand d), and set the control unit master controlto NORM and the function control to NOR-MAL.

b. Disconnect cable No. 8 (fig. 58) from thereceiver-transmitter SUPPR receptacle and re-connect cable No. 8 to the UG-274/U teeadapter on the pulse generator.

c. Turn on all equipment and adjust thesignal level input to the receiver-transmitterto -74 dbm. Measure the width of the secondpulse on the oscilloscope channel A trace, anddetermine the shrinkage as compared to thesecond pulse on the oscilloscope channel Btrace. (The oscilloscope may be calibrated bymomentarily setting test setup switch S6 to theMARK position.)

111. Special Transmitter Reply Pulse TestWhen the transmitter is triggered at the

receiver-transmitter TRIG IN receptacle by a1-usec pulse at a 1-kc pulse repetition rate, thetransmitted reply shall be a single pulse of notless than 0.4 usec in width.

a. Disconnect cable No. 3 (fig. 58) from theuhf signal generator and reconnect it to theTRIG IN receptacle of the receiver-transmitter.Use the test setup configuration (par. 57a andc).

b. Turn on all equipment, except the uhf sig-nal gnerator. Set the pulse generator PULSENO. 2 switch to its OUT position, and adjustthe PULSE RATE dial to 1 kc (pulse width1 usec).

c. Increase the pulse generator FINE ATTNoutput until a transmitted pulse is present onoscilloscope channel B trace. Measure the pulsewidth against the marker generator calibrationon the oscilloscope channel A trace.

112. Decoder Testa. Mode 1. The receiver-transmitter shall

not respond to a mode 1 interrogation when theinterrogation pulse separation is equal to orless than 2 usec, or equal to or greater than4 usec.

(1) Set the control unit master control toNORM, and the function control toMOD (MODE 2 and 3 switches atOFF) Disconnect cable No. 5 (fig.

146

(2)

(3)

(4)

(5)

(6)

58) from switch S6 and connect it toswitch S4 in place of cable No. 9.Check the receiver sensitivity (trig-gering level) in accordance with para-graph 98. Increase the signal input tothe receiver-transmitter by 40 db.Set the test setup switches to the con-figuration described in paragraph 57b,and decrease the interrogation pulseseparation until 50 percent firing isobtained.Set test setup switch S4 to DET(shows interrogating pulses) andmeasure the pulse separation of lowerlimit.Return switch S4 to SUPPR and in-crease the interrogation pulse separa-tion until the 50 percent triggeringpoint is reached.Set switch S4 to DET and measurethe upper interrogation pulse separa-tion limit.

b. Mode 2. The receiver-transmitter shallnot respond to a mode 2 interrogation whenthe interrogation pulse separation is equal toor less than 4 usec, or when equal to or greaterthan 6 usec. Follow the procedures in a(1)through (6) above with the control unit mode2 switch at ON and MODE 3 switch at OFF.Determine the upper and lower mode 2 de-coder 50 percent triggering points.

c. Mode 3. The receiver shall not respond toa mode 3 interrogation when the interrogationpulse separation is equal to or less than 7 usec,or equal to or greater than 9 usec. Follow theprocedures in a (1) through (6) above with thecontrol unit MODE 2 switch at OFF and theMODE 3 switch at ON. Determine the upperand lower mode 3 decoder 50 percent triggeringpoints.

d. Modes 2 and 3. With the control unitMODE 2 and 3 switches at ON, the receiver-transmitter will not respond to interrogationswith pulse separations equal to or less than 2usec, between 6 and 7 usec, and equal to orgreater than 9 usec .

(1) Use the test setup configuration de-scribed in paragraph 57a and e, andoperate the transponder set in allthree positions of the function control.

AGO 10004A

(2)

(3)

Adjust the receiver-transmitter signalinput to 40 db more than normal trig-gering level obtained in paragraph 98.Starting with pulse generator SEPA-RATION control at minimum, slowlyincrease the separation to 10 usecwhile observing the 50 percent trig-gering points.

113. Interrogation Rate TestInterrogation rates of 0.75 and 1 kc will re-

duce receiver sensitivity by more than 30 dbwhen measured at the 100 percent triggeringpoint. (The point at which an occasional hori-zontal sweep occurs on the oscilloscope is notto exceed one trace per second.)

Caution: To prevent overload of the attenu-ator, substitute the lossy line (par. 55a) inplace of the attenuator (fig. 58) when codeselections involve testing with more than fourpulses in a reply train. The attenuator is to beused for receiver-sensitivity measurementsonly.

a. Use the test setup configuration describedin paragraph 57a and e, and the control unit

as follows: the master control to NORM, andthe function control to MOD.

b. Properly interrogate the receiver-trans-mitter at pulse repetition rates of 0.40 to 0.45kc and determine and record the 100 percenttriggering level.

c. Increase the interrogation rate to 0.75 kcand measure and record the signal input re-quired for 100 percent triggering.

d. Increase the interrogation rate to 1 kcand measure and record the signal input re-quired for 100 percent triggering.

e. The difference between the value in b andc, and the value in b and d above is the amountof A.O.C. threshold for the increased interro-gation rates.

114. Random Triggering Rate TestWith the test setup configuration described

in paragraph 57a and d, and the uhf signalgenerator attenuator set to -125 dbm, therandom triggering rate shall not exceed anaverage of 5 replies (any type) over an inter-val of 30 seconds. (Test with several opera-tional categories set up on the control unit.)

AGO 10004A 147

APPENDIX

REFERENCES

Following is a list of references applicable and available to the field and depot maintenancerepairman of Transponder Set AN/APX-44.TM 11-1175 Instruction Book for Radar Test Set AN/UPM-6A and Radar Test Set

AN/UPM-6B.TM 11-1177 Pulse Generator Set AN/UPM-15.TM 11-1242 Crystal Rectifier Test Sets TS-268/U, TS-268A/U, TS-268B/U, TS-

268C/U, TS-268D/U, and TS-268E/U.TM 11-2661 Electron Tube Test Sets TV-2/U, TV-2A/U, and TV-2B/U.TM 11-5083 Electron Tube Test Sets TV-7/U, TV-7A/U, TV-7B/U, and TV-7D/U.TM 11-5126 Power Supply PP-1104A/G.TM 11-5511 Electronic Multimeter TS-505/U.TM 11-5895-217-12 Operation and Organizational Maintenance: Transponder Set AN/APX-

44 .TM 11-5895-217-12P Operator and organizational Maintenance Repair parts and Special ToolS

List, Transponder Set AN/APX-44.TM 11-5895-217-35P Field and Depot Maintenance Repair Parts and Special Tools List, Trans-

ponder Set AN/APX-44.TM 11-6625-203-12 Operation and organizational Maintenance: Multimeter AN/URM-105,

including Multimeter ME-77/U.TM 11-6625-219-12 Operator’s and organizational Maintenance Manual: Oscilloscope AN/

USM-81.

148 AGO 10004A

GLOSSARY

Section I. ABBREVIATIONS

ac----------------alternating currentA.O.C.---------automatic overload controlamp-------------ampereAWG------------ American wire gageCIVIL------------civiliancm---------------centimetercps--------------- cycles per secondcw---------------------continuous wavedb-----------------decibeldbm--------------decibels (referred to 1 milli-

watt)dbv---------------decibels (referred to 1 volt)dc----------------------direct currentDET--------------DetectorIF----------------------intermediate frequencyIFF--------------------Identification Friend or FoeI/P or i/p---------- identification of positionk c - - - - - - - - - - - k i l o c y c l e smc-----------------memegacycles

Section II. DEFINITIONS

Assigned code number. The two or four digitnumber used to identify a pulse reply trainconstruction.

Automatic Overload Control (A.O.C.) Circuitwhich prevents excessive duty cycle of trans-mitter.

Civil reply. Reply trains triggered by civilianground radar interrogations.

Coincidence. The condition in which two sig-nals must arrive simultaneously at a stage topass through the stage.

Decay time. The time required for the voltageto decrease from 90 to 10 percent of peakamplitude on the trailing edge of a pulse.

Decoder. A circuit which responds to a particu-lar interrogation mode and rejects all others.

Differentiator. A short time-constant circuitwhich peaks the input waveform to improvesymmetry.

Duplexer. A device, without tubes or moving

MOD---------------Modified (see SIF)N------------------number of pulses (as used in the

power output formula)Pav-------------average powerpar---------------pulse repetition ratePk-----------------peakak powerRF--------------------radio frequencySIF---------------selective Identification Feature

(MOD)STAY----------------standbySUPER-------------suppressor, suppressionTRIG-------------triggerusec----------------microseconduhf ----------- ultrahigh frequencyv-- - - - - - - - - - -voltvhf---------------very-high frequencyvtvm-------------vacuum tube voltmeterW------------------width, pulse (as used

power output formula)in the

OF UNUSUAL TERMS

parts, which performs transmit-receiveswitching of a common antenna.

Emergency reply. A reply train which retainsthe selected code configuration, but whichmay be repeated to signify unusual circum-stances.

Encoder. A circuit which generates or formsa coded reply in a transponder, also calledcoder.

Fifty percent triggering. The point of sensi-tivity at which the transmitter responds withcomplete replies to one-half the interroga-tions received.

Full triggering. The condition in which atransponder returns the complete reply trainfor each interrogation received.

Identification of position. A reply train whichretains the selected code configuration, but isrepeated or has a pulse added to permit ac-curate radar identification of a specific air-craft.

149

Interrogation. The double-pulse signal receivedby the aircraft transponder from the ground-based interrogator-responder.

Jitter. A momentary pulse separation varia-tion, expressed in microseconds, or a momen-tary amplitude variation expressed in per-cent of peak amplitude.

Main gate pulse. The main synchronizationpulse used throughout the receiver-trans-mitter.

Mode. The identification of interrogation sig-nals; determined by separation between twopulses of an interrogation.

Mode gate pulse. The pulse used to select thecorrect encoder circuit as determined byinterrogation mode.

Modified reply. The series of reply trainswhich differ from previously available re-plies by virtue of multiple code selection(part of Selective Identification Feature).

Normal reply. The reply which is fixed in con-figuration and depends only on interrogationmode.

One hundred percent triggering. The point ofsensitivity at which the transmitter respondswith complete replies to virtually all interro-gations received. Mistriggering must notoccur more than once per second.

Pulse amplitude. The maximum voltage ampli-tude of a pulse or an rf pulse envelope, ex-cluding spike.

Pulse group. The group of pulses that formpart of a complete reply train, groups A, B,C, and D. A group consists of the pulses thatcomprise one digit of the assigned code num-ber.

Pulse position number. The numerical value ofa specific pulse within a pulse group.

Pulse repetition rate. The rate or frequency atwhich interrogations are repeated.

Pulse separation. The time interval betweenadjacent pulses.

Pulse width. The time interval between the 50percent amplitude points on the leading andtrailing edges of the pulse (also called dura-tion).

Reply train. The complete group of selectedpulses, including the first and last framingpulses, in a transmitted reply.

Ringing oscillator. A sine wave oscillator stagewhich provides accurate timing intervals.

Rise time. The time required for the voltageto increase from 10 to 90 percent of peakamplitude on the leading edge of the pulse.

Selective Identification Feature. The additionalselected reply train codes available to assistin identifying specific aircraft in largegroups.

Spike. A narrow pulse, usually less than 0.5usec in width, appearing separately or ontop of a normal pulse.

Spurious reply pulses. Pulses of the reply trainwhich appear in the receiver sections be-cause of internal coupling from the trans-mitter-modulator.

Suppression pulse. A pulse which may be in-jected into receiver to delay response oftransponder to interrogations.

Trigger pulse. A pulse which, when inserted,will cause transmitter to transmit a pulse of0.4 usec or greater in width. Also may referto pulses used within transponder to start astage which is nonoperating.

Zener diode. A crystal rectifier which exhibitsnormal characteristics until reverse voltageexceeds predetermined levels. It then con-ducts back current to maintain a nearly con-stant voltage across it.

150

151

Figure 114. Resist or color code.

CAPACITOR COLOR CODE MARKING(MIL-STD CAPACITORS)

Figure 115. Capacitor color code.

152

Figure 116.153

TM

5895-217-35-98

TM5895-217-35-99

154

Figure 117.

INDEX

Paragraph

Additional equipment required:A l i n e m e n tPullout checks

Additional troubleshooting data Adjustments:

Automatic overload control -------Blocking oscillator and ring

around card.Encoder blocking oscillator Receiver sensitivity --------------Ring around gate multivibratorRinging oscillator ----------------

Alinement:Bench test setup ------------------C o n v e r t e r IF suppressor -------------------Test equipment required Transmitting oscillator -----------

Amplitude, pulse -------------------Antenna:

Removal - - - - - - - - - - - - - - - - - - - - - - - -R e p a i r R e p l a c e m e n t Theory - - - - - - - - - - - - - - - - - - - - - - - - - -

Assigned code number ----------------Automatic overload control:

Adjustment ----------------------Theory__________________________

B+ :Checking circuits Distribution, theory

B a n d w i d t h t e s t Base connections, subminiature tubes..Bench test setup:

Alinement -----------------------P u l l o u t c h e c k Troubleshooting ------------------

Bias:Checking circuits Distribution theory

Blanked cathode follower theoryBlanking amplifier and cathode

follower theory.Block diagrams:

Blocking oscillator and ringaround card.

C o n t r o l c i r c u i t s Converter subchassis -------------Decoder card --------------------Gate generator card --------------IF-suppressor subchassis _

85b9b73

9093

91959492

85c87868588

17b

5d846a38

21a

9028e

544199

73c

85c9c55

5442

28d28c

31a

4426a29a30a27a

Page

1336

117

139140

139141141139

133136133133137

11

3132

35714

13933

7360

142117

1336

76

73613232

41

6320333821

Paragraph Page

Block diagrams-ContinuedMode reply selector card 35a 48Modulator-transmitter ------------ 37a 54Receiver-transmitter ------------- 25 16Ringing oscillator and coincidence 36a 50

card.Transponder Set AN/APX-44_____ 23-25 15-16Video amplifier card -------------- 28a 31

Blocking oscillator and ring aroundcard:

Adjustments --------------------- 91,94 139,141Block diagram theoryGated amplifier ------------------G e n e r a l R e p a i r Ring around gate multivibrator----Theory -- - - - - - - - - - - - - - - - - - - - - - - - -Transformer data Trigger amplifier-blocking

oscillator.Troubleshooting ------------------Voltage and resistance

measurements.Waveforms ----------------------

Blocking oscillator V151:A d j u s t m e n t Theory -- - - - - - - - - - - - - - - - - - - - - - - - -

BNC connector installation

C connector installation ----------------Cable fabrication:

Bench test -----------------------Coaxial - - - - - - - - - - - - - - - - - - - - - - - - -

Card removal, with tool Category, reply coding byCavity, transmitter repairs Center frequency test Checking primary power, B+ and

bias circuits.Checks:

Functional:C o n c l u s i o n General ---------------------Power requirements _P r o c e d u r e Test equipment required ------Test setup ------------------

Periodic --------------------------Pullout:

Additional equipment requiredBench test set ----------------Check procedures Test equipment required ------

31a 4131d 4431a 41

74-76 119,12031c31

67c31b

6767b

67c

9336f- - -

- - -

9c55a- - -

2079

10054

151011141213

2

9b9c9d9b

4241

10541

105105

105

1405478

79

6768912

123143

73

101010101010

2

6666

155AGO 10004A

Paragraph PageParagraphCIVIL:

F u n c t i o n s Reply codes------------------------- 20d

Code:Group letter ---------------------------- 21bReply:

By assigned code number ------------ 21By category -------------------------- 20Switching card trouble- 70

shooting.Coincidence detector theory ------------ 36eConnector, receiver-transmitter, repair 82

or replacement.Control circuits:

Block diagram ---- - - - - - - - - - - - - - - - 44Theory ------------------------------------- 45,46

4 6 h - j

Control unit:Continuity check -----------------Removal - - - - - - - - - - - - - - - - - - - - - - - -Repairs -- - - - - - - - - - - - - - - - - - - - - - - -Replacement - - - - - - - - - - - - - - - - - -

Converter subchassis:Alinement ------------------------B lock d iagram - - - - - - - - - - - - - -Crystal oscillator-----------------------G e n e r a l - - - - - - - - - - - - - - - - - -Harmonic generator and selector-Mixer -----------------------------Preselector -----------------------R e p a i r s - - - - - - - - - - - - - - - -Theory -- - - - - - - - - - - - - - - - - - - - - - - - -T r i f l e r - - - - - - - - - - - - - - - -Troubleshooting ---------------Voltage and resistance measure-

ments.

Decay time, pulse ---Decoder card:

Block diagram ------------------Delay line resistances ------------G e n e r a l - - - - - - - - - - - - - - - - - -Modes 1, 2, and 3 decoders -------Output distribution circuit -------Theory -- - - - - - - - - - - - - - - - - - - - - - - -Troubleshooting -----------Voltage and resistance measure-

ments.W a v e f o r m s - - - - - - - - - - - -

Delay line DL601 resistances ---------Delay test ----------------------------Differentiator theory --------------------Diode:

Co lor cod ing - - - - - - - - - - - - - - - -K i c k o f f - - - - - - - - - - - - - -Rectifier data. ----------------Suppressor -----------------------

525b836c

8726a26c26a26e26f26b

7726

26d62

62b

17e

29a65d29a29b29c2965

65b

65c73a10736f

73d27d73d27f

Switching ---------------------------32-34Troubleshooting ------------------ 73d

Disassembly:C o n v e r t e r - - - - - - - - - - - - - - 77aPrinted circuit card ---------------- 76aTransmitter cavity -------------- 79b

156

Page

6613

14

1412

112

52131

6363,65

723

1323

136202020212120

12220219393

11

33101

33343433

101101

101117144

54

11726

11728

44-47117

122120123

Distribution theory:B+____________________________Bias --- - - - - - - - - - - - - - - - - - - - - - - - - - -Decoder output -------------------P r i m a r y p o w e r - - - - - - - - - - - -

Driver and ringing oscillator theory-------Driver theory V152-------------------Duplexer; theory --------------------

EMER, master control circuits -----------Emergency:

Functions:CIVIL -----------------------MOD-- - - - - - - - - - - - - - - - - - - - - -NORMAL -------------------

Reply codes ---------------------Encoder blocking oscillator:

Adjustments ----------------------Theory -- - - - - - - - - - - - - - - - - - - - - - - - -

External maintenance ------------------

Fabrication of bench test cable -----------Final testing:

D e c o d e r - - - - - - - - - - - - - - - -Interrogation rate ----------------Main gate pulse characteristics----P u r p o s e - - - - - - - - - - - - - - - - - - -Random triggering rate --------------Receiver:

B a n d w i d t h - - - - - - - - - - - - -Center frequency ------------Image response----------------Sensitivity --------------------Sensitivity level test---------------

Receiver-transmitter:Delay -- - - - - - - - - - - - - - - - - - - - - -Pulse reply ----------------------Range jitter----------------------------

Second pulse width-------------------Single interrogation pulse --------Test equipment required----------------Test setup --- - - - - - - - - - - - - - - - - -Transmitter:

Frequency ------------------Power output ----------------------Special reply ----------------

First and second clippers, theory -----------First video amplifier, theory------------Framing pulse ------------------------Functional check:

Conclusion ----------------------General - - - - - - - - - - - - - - - - - - - - - - - - -Procedure -----------------------Test equipment required ----------------T e s t s e t u p - - - - - - - - - - - - - - - - -

Function control circuits ---------------Fuses, removal ----------------------Gated amplifier theory ---------------

Gate generator:Block diagram -------------------G e n e r a l - - - - - - - - - - - - - - - - -

4142

29c43

36b37c37f

45d

46j46g46d20e

9131b

3

9c

112113103

96114

99100102

98101

107108106110109

9797

10510411136c27c20c

1510141213465e

31d

30a30a

60613462515556

63

66666513

13941

2

6

146147143142147

142143143142143

144144144145145142142

144143146

512813

101010101065

344

3838

AGO 10004A

ParagraphGate generator-Continued

Main gate multivibrator ---------Model gate multivibrator --------Mode 2 and 3 gate multivibrators-----Theory - - - - - - - - - - - - - - - - - - - - - - - - -Troubleshooting------------------Voltage and resistance measure-

ments.Waveforms---- - - - - - - - - - - - - - - - - - -

Harmonic generator and selector,theory.

High voltage power supply:R e p a i r s - - - - - - - - - - - - - - -T h e o r y - - - - - - - - - - - - - - - - - - - - -Troubleshooting-----------------

Identification, position:Functions:

CIVIL- - - - - - - - - - - - - - - - - - - - - -MOD-- - - - - - - - - - - - - - - - - - - - - -NORMAL- - - - - - - - - - - - - - - - - -

Reply codes---------------------------IF-suppressor subchassis:

Adjustment (sensitivity)---------Alinement procedure ------------b l ock d iagram - - - - - - - - - - - - - -Fifth and sixth IF amplifiers-------------First and second IF amplifiers ----First video amplifier and cathode

follower.G e n e r a l - - - - - - - - - - - - - - - -Repair ----Second video amplier and cathode

follower.S u p p r e s s o r - - - - - - - - - - - - - - -Theory - - - - - - - - - - - - - - - - - - - - - - - - - -Troubleshooting-- - - - - - - - - - - - - -Voltage and resistance measure-

ments.Image response test-- - - - - - - - - - - - -Internal maintenance -----Interrogation:

CharacteristicsM o d e - - - - - - - - - - - - - - - - - - - - - - - - - -Pulse test--------------------Pulse width test ------------------Rate --------------------------Rate test ---------------------------S igna l path - - - - - - - - - -

Interunit troubleshooting:Chart -- - - - - - - - - - - - - - - - - - - - - - - - - -Procedures -----------------------

Isolation procedures ------------------

J i t ter t es t , range - - - - - - - - - - - - - - -

Localization procedures ---------------Localizing troubles -------------------LOW position of master control,

circuits.

AGO 10004A

30d30b30c3066

66b

66c

26e

813972

46i46f46d20e

9486

27a27d27b27e

27a78

27g

27f2763

63b

1028

18b18a10911018c113

23

515060

106

48c58

45d

57

Page

41404038

104104

104

21

130

113

66666513

141133

21262428

21123

30

28219898

1435

1211

145145

12147

15

707093

144

678263

Low voltage power supply:R e p a i r s - - - - - - -T h e o r y - - - - - - -T r o u b l e s h o o t i n g - - - - - - -

Paragraph Page

Main gate characteristics test-------Main gate multivibrator theory--------Main rectifier board, removal--------Maintenance:

External--- - - - - - - - - - - - - - - - - - - - - -I n t e r n a l - - - - - - - - - - - -

Master control circuits-----------Materials required for troubleshootingMOD function control circuits------Model:

D e c o d e r t h e o r y - - - - - - -Gate multivibrator theory -----------Reply code switching card, theoryReply selector theory ------------T r o u b l e s h o o t i n g - - - - - - - - - - - -

Mode 2:Decoder theory ------------------Gate generator theory ------------Reply code switching card; theoryReply selector theory----------Switching arrangement -------Troubleshooting ------------------

Mode 3:D e c o d e r t h e o r y - - - - - - - - - - - -Gate multivibrator theory ----------Reply code switching card, theory---Reply selector theory -----------Troubleshooting ------------------

Mode reply selector card:Block diagram-------------------G e n e r a l - - - - - - - - - - - - - - - - - - - - -Main gate amplifier --------------Modes 1, 2, and 3 reply selectors--Reply train amplifier -------------Theory------------------------------T r o u b l e s h o o t i n g - - - - - - - - - - -Voltage and resistance measure-

ments.W a v e f o r m s - - - - - - - - - - -

Modulator-transmitter:Adjustments--- - - - - - - - - - - - - - - - - - -A l i g n m e n t - - - - - - - - - - - - -B lock d iagram- - - - - - - - - - - - - - -D r i v e r - - - - - - - - - - - - - -Duplexes--- - - - - - - - - - - - - - - - - - - - - -G e n e r a l - - - - - - - - - - - - - -M o d u l a t o r - - - - - - - - - - - - -R e p a i r s - - - - - - - - - - - - -Theory - - - - - - - - - - - - - - - - - - - - - - - - -Transmitting oscillator-----------Trigger amplifier and blocking

oscillator.T r o u b l e s h o o t i n g - - - - - - - - - - - -Voltage and resistance measure-

ments.W a v e f o r m s - - - - - - - - - - - - - -

814072

10330d81c

38

4549b

I46e–g

29b30b

3235b

70

29b30c

3335b

2270

29b30c

34

70

35a35a35d35b35c

3568

68b

68c

9388

37a37c37f37a37d

8037

37e37b

71

71c

13058

113

14341

131

25

6369

65-66

34404449

112

3440454914

112

34404749

112

484850495048

107107

107

140137

5455565455

125545655

112112

112

157

ParagraphMounting:

Removal - - - - - - - - - - - - - - - - - - - - - - - - - 5 CReplacement - - - - - - - - - - - - - - - - - - - - - 6 b

NORMAL :Function control circuits --------- 46b-dReply code switching circuits:

Mode 1---- - - - - - - - - - - - - - - - - -Mode 2---- - - - - - - - - - - - - - - - - -M o d e 3 - - - - - - - - - - - - - - - - -

Number:Assigning code -------------------Pulse position -------------------

Operational check - - - - - - - - - - - - - - - -Organizationof troubleshooting

procedures.

Periodic check:Functional ------------------------Operational ------------------------Pullout ---------------------------Timing --- - - - - - - - - - - - - - - - - - - - - - - -

Power output test --------------------Power requirements for functional

check.Power supply:

High voltage:R e p a i r - - - - - - - - - - - - -Theory ------------------------Troubleshooting --------------

Low voltage:Repair -----------------------Theory---- - - - - - - - - - - - - - - - - - -Troubleshooting-------------

P r e s e l e c t o r t h e o r y - - - - - - - - - - - -Preventive maintenance:

External --------------------------Check:

Functional check -------------Operational -----------------Periodic ----------------------Pullout ----------------------

Internal ----------------------------Removal -------------------------Replacement ----------------------

Primary power distribution -----------Printed circuit card repairs --------------Pulse:

A m p l i t u d e - - - - - - - - - - -D e c a y t i m e - - - - - - - - - - - - -G e n e r a l - - - - - - - - - - -R e p l y t e s t - - - - - - - - - - - -Rise time ------------------------S e p a r a t i o n - - - - - - - - - - - - - - -Test, single interrogation -----------Test, special reply -----------------Width ---- - - - - - - - - - - - - - - - - - - - - - -Width test, second interrogation

pulse.

Random triggering test ---------------

158

32b33b34b

21a21c

348

10-15392

10411

813972

814072

26b

3

10-15329856

4376

17b17e17a10017d17f10911117c110

114

Page

33

65

454647

1414

267

10252

14310

13057

113

13058

11320

2

10225523

62120

111111

1431111

145146

11145

147

Receiver:Sensitivity adjustment --------------Tests:

Bandwidth---- - - - - - - - - - - - - - -Center frequency ------------Image response--------------------Sensitivity ------------------Sensitivity level selection-------

Receiver-transmitter:

Paragraph Page

A d j u s t m e n t s - - - - - - - - - - - - - -A l i n e m e n t - - - - - - - - - - - - - -Alinement test setup -------------Bench test setup:

Pullout fleck---------------Troubleshooting -------------

B l o c k d i a g r a m - - - - - - - - - -Preventive maintenance -----------Removal -------------------------R e p a i r - - - - - - - - -Replacement ----------------------Tests:

De lay - - - - - - - - - - - - - - - - - - - - - - -Pulse reply------------------Range jitter-----------------

Troubleshooting:C h a r t - - - - - - - - -Procedures--- - - - - - - - - - - - - - - -

Rectifier:Circuits:

+125-volt---------------------150 -vo l t - - - - - - - - - - - - - - - - - - -+300-volt-- - - - - - - - - - - - - - - - - -+600-volt-- - - - - - - - - - - - - - - - - - -+ 1 , 2 0 0 - v o l t - - - - - - - - - -Data - - - - - - - - - - - - - - - - - - - - - - - -

R e l a y m e a s u r e m e n t s - - - - - - - - -Removal for maintenance and repair--------------Repair:

Antenna --- - - - - - - - - - - - - - - - - - - - - -Control unit ---------------------G e n e r a l - - - - - - - - - - - -Receiver-transmitter:

Connector--- - - - - - - - - - - - - - - - -Converter--- - - - - - - - - - - - - - - - -IF-suppressor subchassis ------M o d u l a t o r - - - - - - - - - - - - - - - -Power supply--- - - - - - - - - - - -Printed circuit cards ---------Transmitter cavity ------------

Soldering instructions ------------Replacement after maintenance and

repair.Reply:

Code selection:Mode 1---- - - - - - - - - - - - - - - - - -Mode 2---------------------M o d e 3 - - - - - - - - - - -

Coding:By assigned code number--------------By operational category---------

95 141

99 142100 143102 143

98 142101 143

89-95 139-14185-88 133-137

85c 133

9c 655 7625 16

1-9 2-55a 2

74-84 119-1326d

107108106

59b53

40c40d39c39d39e73d73b

5

848374

8277788081767975

6

323334

2120

5

144144144

9273

5960585858

117117

2

132132119

131122123125130120123119

3

444547

1412

AGO 10004A

ParagraphReply-Continued

Signal path --------------------------Transmitted -----------------

Reply train amplifier theory -------------------------Ring around gate multivibrator:

A d j u s t m e n t - - - - - - - - - - - - - - - - -T h e o r y - - - - - - - - - - - - - - - -

Ringing oscillator and coincidencecard:

A d j u s t m e n t - - - - - - - - - -B l o c k d i a g r a m - - - - - - - - - - - - -Blocking oscillator ----------------C l i p p e r s - - - - - - - - - - - - - - - -Coincidence detector ---------------Differentiator --------------------Driver and ringing oscillator ---------T h e o r y - - - - - - - - - - - - - - -Troubleshooting ---------------Voltage and resistance measure-

ments.W a v e f o r m s - - - - - - - - - - - - - - - -

Scope of manual-- - - - - - - - - - - - - - - - - -Second interrogation pulse width test-----Second video amplifier ana cathode

follower theory.Sectionalization----------------------Selective identification feature ----------Sensitivity:

Adjustment---- - - - - - - - - - - - - - - - - - -Level selection test --------------Receiver sensitivity test ----------

Separation, pulse --------------------Single interrogation pulse test ------------Soldering instructions----------------Special transmitted reply pulse test ---Spike suppressor and inverter theory-----Subminiature tube base connections ---Suppressor theory------------------Switch circuit test points, mode 2-----Switching:

Arrangement, mode 2-------------Card troubleshooting -------------

2419

35c

9431e

9236

36f36c36e36d36b

3669

69b

69c

111027g

48b20c

95101

9817f109

7511128b73c27f73e

2270

Reply code theory -------------------- 32, 33,

Techniques, pulse - - - - - - - - - - - - - - -Test equipment required:

A d j u s t m e n t s - - - - - - - - - - - - - - - - -Alignment--- - - - - - - - - - - - - - - - - - - -F i n a l t e s t - - - - - - - - - - - - - - - -Functional check ----------------Pullout cock--- - - - - - - - - - - - - - - - - -Troubleshooting ------------------

Test setup:A l i n e m e n t - - - - - - - - - - - - - - - - - -Functional check -------------------Pullout check ---------------------Troubleshooting ------------------

Theory of operation:Antenna --- - - - - - - - - - - - - - - - - - - - - -

AGO 10004A

34

17

8985a

97129d49

85139c49

38

Page

161250

14144

13950545152515150

109109

111

2145

30

6713

141143142

11145119146

3111728

118

14112

44, 45,47

11

139133142

106

68

13310

668

57

ParagraphTheory of operation-Continued

Blocking oscillator and ring 31around card.

Control circuits ----------------------- 44-46Converter subchassis -------------D e c o d e r c a r d - - - - - - - - - - - - -Gate generator card -------------High voltage power supply --------IF-suppressor subchassis ---------Low voltage power supply --------Mode reply selector card -------------Modulator-transmitter -----------Receiver-transmitter block --------Ringing oscillator and coincidence

card.Transponder set block ----------Video amplifier card --------------

Transformer replacement ----------------Transistor:

Replacement ---------------------Troubleshooting -----------------

Transmitted replies:Characteristics ------------------------Signal path ---------------------

Transmitter tests:Frequency -----------------------Power output --------------------Special reply --------------------

Transmitting oscillator:Alinement--- - - - - - - - - - - - - - - - - - - - -Repairs - - - - - - - - - - - - - - - - - - - - - - - - -Theory - - - - - - - - - - - - - - - - - - - - - - - - -

Trigger amplifier and blockingoscillator theory.

Trigger amplifier and encoder blockingoscillator theory.

Tripler theory-----------------------Troubleshooting:

Additional data ------------------Bench test setup -----------------Blocking oscillator and ring

around card.Control unit-- - - - - - - - - - - - - - - - - - -Converter subchassis -----------------------Decoder card --------------------Gate generator card ---------------------General instructions ------------------IF-suppressor subchassis ---------------I n t e r u n i t - - - - - - - - - - - - - - -Isolation:Procedures-----------------------Test equipment ------------------Localizing methods -----------------Mode reply code switching cards..Mode reply selector card ----------Modulator-transmitter ------------Power supplies -----------------Procedures, organization -----------------Receiver-transmitter, chart --------Ringing oscillator and coincidence

card.

26293039274035372536

23,2428

81a

81f72d

1924

105104111

8879

37e37b

31b

26d

735567

526265664763

50, 51

60615870687172485969

Page

41

63-6520333857215848541650

15, 1631

130

131115

1216

144143146

137123

5655

41

21

11776

105

7293

101104

679870

939382

112107112113

6788

109

159

Troubleshooting-ContinuedTest equipment required ---------Video amplifier card --------------

Video amplifier card:Adjustments (A. O. C.)----------A. O. C. amplifier and rectifier ------Blanked cathode follower ---------Blanking cathode follower and

amplifier.Block diagram --- - - - - - - - - - - - -Spike suppressor and inserter---T h e o r y - - - - - - - - - - - - - - - - - - -Troubleshooting--------------------Voltage and resistance measure-

ments.Voltage and resistance measurements:

Blocking oscillator and ringaround card.

Converter subchassis--------------------Decoder card -----------------------Delay l ine - - - - - - - - - - - - - - - - - - - - -Gate generator card -------------

Paragraph

4964

9028e28d28c

28a28b

2864

64b

67b

62b65b73a66b

Page

68100

139333232

313131

100100

105

93101117104

Voltage and resistance measurements-Continued

IF-suppressor subchassis ---------Mode reply selector card --------Modulator-transmitter --------------Relays -- - - - - - - - - - - - - - - - - - - - - - - - -Ringing oscillator and coincidence

card.V i d e o a m p l i f i e r c a r d

Waveforms:Blocking oscillator and ring

around card.Decoder card ------------------Gate generator card-------------Mode reply selector card --------------Modulator-transmitter-------------------Power supplies-----------------------Procedures for taking----------------Ringing oscillator and coincidence

card.Width:

Pulse ----------------------------Test, second interrogation pulse

By Order of Wilber M. Brucker, Secretary of the Army:

Official:R. V. LEE,

Major General, United States Army,The Adjutant General.

Distribution:Active Army:

160

Paragraph

63b68b71b73b69b

64b

67c

65c66c68c71c72c58c69c

17c110

Page

98107112117109

100

105

101104107112115

82111

11145

L. L. LEMNITZER,General, United States Army,

Chief of Staff.

To be distributed in accordance with DA Form 12-7 requirements for TM 11 Series (UNCLA) plus thefollowing additional formula:

ASA (2)Tech Stf, DA (1) except

CSigO (20)CofT (20)

USA Abn & Elct Bd (1)USA Arctic Test Bd (2)MDW (1)Seventh us Army (4)

EUSA (4)Corps (2)USMA (2)USASCS (900)Units org under fol TOE:

11-155 (2)11-500 (AA-EE) (2)11-587 (2)

NG: State AG (3) ; units-same as Active Army except allowance is one copy to each unit.USAR: None.For explanation of abbreviations used, see AR 320-50.

U.S. GOVERNMENT PRINTING OFFICE : 1 9 9 3 O - 3 4 2 - 4 2 1 ( 8 0 0 6 7 )

AGO 10004A

Figure 5.

Figure 5.

Figure 5

TM5895-217-35-4

Figure 58Figure 58.

Figure 76.

TM5895-217-35-101

Figure 76

Figure 78.

TM5895-217-35-102

Figure 78

Figure 80.

Figure 80

TM5895-217-35-103

Figure 82

Figure 82.

Figure 84.

Figure 84

TM5895-217-35-105

Figure 86

TM5895-217-35-106

Figure 86.

Figure 87.

Figure 87

TM5895-217-35-107

Figure 89

Figure 89.

Figure 124

Figure 124.

Figure 124.

Figure 125

Figure 125.

Figure 125.

Figure 126

Figure 126.

Figure 126.

Figure 132

Figure 132.

Figure 132.

019108 - 000

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