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SENDER A.M. TransmittersSENDER A.M. Transmitters
SENDER S.A.SENDER
SENDER S.A.SENDER S.A.
• Company was created in 1997 by a group of engineers and technitians with long experience in Solid state A.M. Transmitters.
• Located in Santiago Chile, with 25 employes. 40% of them are shareholders. • Main activity: Design and manufacturing of A.M. transmitters, antenna tuning units, duplexers and triplexers.
• First transmitter in operation Nov 1997.
• Transmitters sold up to now:127 from 1 KW to 12.5 KW.
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Product LineProduct Line
AM 1500 SS 1.5 KW/1.1 KW, single phase / 2 power amplifiers
AM 3000 SS 2.25 KW/3KW, single phase or 3 phase / 4 power amplifiers.
AM 7500 SS 5.5 KW/ 7.5 KW, 3 phase or single phase / 7 power amplifiers. AM 15000 SS 11 KW/13 KW,3 phase / 14 power amplifiers
AM 25000 SS 22 KW/26KW, 3 phase / 28 power amplifiers
A.T.Us for 1.5 KW, 3 KW,7.5 KW, 13 KW and 26 KW
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Product highlightsProduct highlights
• Solid State. Modular / redundant architecture• High efficiency. PWM & class D R.F. amplifiers• Hot plug in power amplifiers with Mosfets.• Simple design with standard components.• Totally rustproof cabinet made of iridated aluminum with stainless steel hardware.• Excellent specs and audio quality.• Outstanding factory support.• Very competitive price.
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Basic specificationsBasic specifications
Frequency range: .53 MHZ to 1.7 MHZ.
Input voltage: 110V or 220 V single phase, 220V or 380V 3 ph+or - 10%. Line frequency 47HZ to 63 HZ.
Efficiency: 75% or better for single phase transmitters, 80% or better for 3 phase transmitters.
Frequency response: Better than +or- 1 dB 30 Hz to 10 KHZ.
Distortion: Less than 1% at nominal power and 90% modulation.
Harmonics and spurious:- 73 dB or better for AM 1500 SS, - 80 dB or better for other models.
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Frequency stability:+- 5 Hz.
Output impedance: 50 Ohm
Dimentions and weigths: AM 1500 SS W=44 cm,H=62.5cm D=60 cM , 100 Kg. AM 3000 SS W=44 cm,H=65.5cm D=60 cM , 160 Kg. AM 15000 SS W=80 cm,H=181cm D=81 cM , 500 Kg.
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Standard features: 2 power level with independient adjustment and modulation autotracking. Start, stop,power level selection and power level adjustment remotely controled. Automatic alarm reset. Positive and negative limiter.
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Basic block diagramBasic block diagram
Synth
PWM
Combiner
An
A2
A1
OutputFilter
ControlPWR
Supply
Out
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Relationship with Relationship with RICHARDSON ELECTRONICSRICHARDSON ELECTRONICS
• Exclusive representation for Asia and other specific countries.
• Joint project to manufacture transmitters in U.S.A.
• Sender sells Omnicast F.M. Transmitters in Latin America.
• Excellent level of personal contacts .
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Near future projectsNear future projects
• FCC type acceptance.
• Frequency agile 1.5 KW transmitter.
• IBOC compatibility.
• Inboard audio processor and modulation monitor.
• Higher power amplifiers
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Reliability in A.M. stations
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IntroductionIntroduction
• Harmonic set of:– Transmitter– Radiating system– Energy System– Auxiliary Equipment
Station Concept
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Experience with stations using Solid Experience with stations using Solid State A.M. TransmittersState A.M. Transmitters
• Very high reliability if precautions related with the following topics are considered: Antenna discharges
A.C. Source transients and discharges
A.C. Source voltage limits
Load stability
Interference from nearby stations
Reliability is reduced in unprotected stations
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A.C.
Basic elements of a station Basic elements of a station
GROUND PLANE
ATUTX
STL RX
RF
Audio &Rem. Ctrl.
T.P.
H.V
TRANSF.DISTR.BOARD
ANTENNA
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TRANSMITTER BASIC BLOCKSTRANSMITTER BASIC BLOCKS
• POWER SUPPLY• PWM MODULATOR• R.F. DRIVER• CLASS D or E• R.F. OUTPUT FILTER• CONTROL,PROTECTIONS,SIGNALING• EXTERNAL INTERFACE
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PWM MODULATORPWM MODULATOR
• GENERATES D.C + A.C. VOLTAGE FOR THE R.F. AMP.
• SWITCHING DEVICE, HIGH EFFICIENCY• A FILTER IS NEEDED TO ELIMINATE
SWITCHING FREQUENCIES• CONMUTATION FREQUENCY IS 72 KHZ.
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PWM PWM (PULSE WIDTH MODULATION)(PULSE WIDTH MODULATION)
SIMPLIFIED DIAGRAM:
D.C. SUPPLY Switch(Mosfet) PWM FILTER LOAD
R.F. AMPLIFIER
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PWM BASIC OPERATIONPWM BASIC OPERATION
Filtered output voltagePWM waveform
1)
2)
3)
4)
S
V RL
• Between 1) y 4) duty cycle is increased• Mean voltage in the load increases proportionally• A filter is required to remove high frequency components
F = 72 kHz
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PWM Frequency spectrumPWM Frequency spectrum
72 kHz 144 kHz
D.C Component
Audio
Amplitude
Frecuency
PWM 0°
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PWM Frequency spectrumPWM Frequency spectrum
72 kHz144 kHz
D.C. component
Audio
Amplitude
Frecuency
72 KHZ components out of phase
PWM 180°
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PWM filter diagramPWM filter diagram
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PWM filter frequency responsePWM filter frequency response
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PWM filter response sensibility PWM filter response sensibility to load changesto load changes
Rload +/- 15%
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Load change consequencesLoad change consequences
• With reduced load (Rload< Rnominal) transmitter will produce high frequency submodulation
• With increased load (Rload>Rnominal) transmitter will show high frequency overmodulation
• Distorsion will increase if filter is not propperly loaded.
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Modulated class D R.F. Amplifier.Modulated class D R.F. Amplifier.
T1
T2
RLT3
T4
PWM filter
+V
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Class D r.f. Amplifier diagramClass D r.f. Amplifier diagram
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Class D Bridge parasitic Class D Bridge parasitic elementselements
RL
V+
CdsCdsCgd
Cgs
CdsCdsCgd
Cgs
Ciss = Cgs + Cgd Crss = Cgd Coss = Cds + Cgd
CdsCdsCgd
Cgs
CdsCdsCgd
Cgs
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Mosfets driveMosfets drive
T1
T2
RLT3
V+
Vgs(thr)
Vgs peak = 13V
Dead time
Vgs
timeT4
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R.F. drive circuitR.F. drive circuit
Cgs
Drive signalLs Cs
Lp
• Ls and Cs series resonant
• Lp paralel resonant with mosfet input capacitance (Partially)
MOSFET drive
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Class D bridge current pathsClass D bridge current paths
T1
T2
RLT3
T4
V+
T1
T2
RLT3
T4
V+
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Class D bridge undisered current Class D bridge undisered current paths.paths.
T1
T2
RLT3T3
T4T4
V+V+
T1T1
T2T2
RLT3
T4
V+V+
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Class D Amplifier basics.Class D Amplifier basics.
• Low impedance driver required for:– Fast switching– Low Vgs modulation by Crss
• Tuned load to produce sinusoidal current
• High efficiency (>95 %)
• Duty cycle should be < 0.5– Avoid transversal currents – Coss charge and discharge through Rl
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Class D R.F. Amp typical Class D R.F. Amp typical waveforms.waveforms.
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MOSFET characteristicsMOSFET characteristics
• No secondary breakdown
• positive temperature coeff. Of Rdson (Simplify parallel operation)
• Voltage controled device (Vgs)
• Driver impedance dependent switching times.
• Intrinsic antiparallel diode
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IRFP350 MOSFETIRFP350 MOSFET
• Rdson = 0.3 ohms• Vdss = 400 Vdc• Vgs = +/- 20 Vmax Vth = 3 V Vsat = 9 V• Id = 16 A @ Tc=25ºC 10 A @ Tc=100ºC• Idmax = 64 A• Capacitance @ f=1MHz, Vds=25V , Vgs=0V
– Ciss = 2600 pF (2400 pF for Vds>40V)– Coss = 660 pF (200 pF for Vds>40V)– Crss = 250 pF (50 pF for Vds>40V)
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Class D amplifier exampleClass D amplifier example
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Class D SimulationClass D Simulation(1/2 bridge,Vmax<400x.75/2.5)(1/2 bridge,Vmax<400x.75/2.5)
• Cicuit data– Vdc = 110 V– F = 1600 kHz– d = 0.43– Transistor IRFP350
• Rdson = 0.3 ohms
• Ton = 16 ns
• Toff = 40 ns
• Coss = 200 pF
– L2 = 7.04 uH– C2 = 1.55 nF
• Operational data– RL = 15 ohms– Po = 132.36 W– h = 97.93 %
•Transistor stresses– Vmax = 110.81 V– Imax = 4.12 A– Pdis = 0.70 W x2
(1.4 Wtotal)
*Simulated with HB plusfrom Design Automation
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Class E Amplifier diagramClass E Amplifier diagram
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Class E amplifier exampleClass E amplifier example
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Class E amplifier basics.Class E amplifier basics.
• R.F.Choke large enough to produce constant current
• High Q series resonant circuit to produce sinusoidal current
• Vds y dVds/dt =0 prior to starting conduction• High efficiency (>95%)
– if special high voltage transistors with low Rdson are used
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Clase E WaveformsClase E WaveformsSENDER
Clase E SimulationClase E Simulation(Vmax<400x.75/2.5)(Vmax<400x.75/2.5)
• Circuit Data– Vdc = 33 V– F = 1600 kHz– d = 0.48– Transistor IRFP350
• Rdson = 0.3 ohms• Ton = 16 ns• Toff = 40 ns• Coss = 200 pF
– L1=12.3uH L2=3.7uH– C1= 4.1nF C2=4.9nF
• Operational Data– RL = 7.3 ohms– Po = 125.27 W– h = 90.53 %
• Transistor stresses– Vmax = 118.79 V– Imax = 9.84 A– Pdis = 6.55 W x2
(13.1 Wtotal)
*Simulated with HEPA Plus from Design Automation
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Passband Output filterPassband Output filter
• Reduce R.F. Harmonics– High third harmonic att > 80 dB– Medium second harmonic att. > 40 dB– Higher harmonics att > 70 dB
• Permits impedance matching between amplifier and load.
• Atenuates low frequency components (Lightning protection)
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Output filterOutput filter
• Design oriented to protect R.F.amplifier– Low frequency attenuation– Inductor input– Strategically located sensors:
• Spark Gap °Transient suppressor• SWR °Overpower• Overcurrent °Phase• Input transient suppressor(Active or pasive)
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Output filter diagramOutput filter diagram
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Output filter frequency responseOutput filter frequency response
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Real and imaginary part of filter Real and imaginary part of filter input impedanceinput impedance
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Protections integrated in the Protections integrated in the output filteroutput filter
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Posible Transmitter AgresionsPosible Transmitter Agresions
• Antenna– Impedance change and discharges
• A.C. Supply – Voltage variation and transients
• Program signal– Level variations and transients
• Ground– Transfered potentials and high ground
currents
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Antenna related problemsAntenna related problems
• Impedance change– Low heigth antennas are particularly
unstable
• Restricted bandwidth
• Interference from other stations
• Discharges
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Short antenna exampleShort antenna example
60 m tower operating at 700 kHz
ZL = 8 - j160Q = 20Electrical length = 50.4º
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Type T -90º Standard A.T.U.Type T -90º Standard A.T.U.
4.55uHj20
40.9uHj180
ZL8-j160
11.37nF-j20
Zin50+j0
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A.T.U.Sensibility to antenna A.T.U.Sensibility to antenna impedance changesimpedance changes
Change in XL (+/- 10 ohm=6%)if ZL=8-j150 Zin=19.5-j24.4 SWR=3.26if ZL=8-j160 Zin=50+J0 SWR=1if Zl=8-J170 Zin=19.5+j24.4 SWR=3.26
Change in RL ( +/- 1 ohm =12.5%)if ZL=7-j160 Zin=57.1+j0 SWR=1.14if ZL=9-j160 Zin=44.4+j0 SWR=1.14RL and XL simultaneous variationif ZL=7-j150 Zin=18.8-j26.8 SWR=3.52if ZL=7-j170 Zin=18.8+j26.8 SWR=3.52if ZL=9-j150 Zin=19.9-j22 SWR=3.10if ZL=9-j170 Zin=19.9+j22 SWR=3.10
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Complex A.T.U. (dual T)Complex A.T.U. (dual T)
j5 j145
ZL8-j160j37
Zin50+j0
j50.5
-j92.5
-j44.9
Variations in XLif ZL=8-j150 Zin=50+j62.5 SWR=3.26if ZL=8-j160 Zin=50+j0 SWR=1.00if ZL=8-j170 Zin=50-j62.5 SWR=3.26
Note: SWR of 8+/-j10 refered to a 8+j0 is 3.26 !
20°-20°
20-J13
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Load ladderLoad ladder
RF amplifiers
Zn
Z1
Extreme values for SWR 1:1.5, refered to 50 Ohm, are:33.3+j0 75.0+j050-j20.4 50+j20.4
1
n
combiner filter A.T.U.
Antenna50 Ohm
15 Ohm
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Load variation effectsLoad variation effects
Class D amplifierClass D amplifier
Load VSWR (%) P (1/2bridge)
Vmax (V) Imax (A)
15 1 97.93 132.36 110.81 4.1215-j6.1 1.5 96.55 151.92 109.80 57.7715+j6.1 1.5 97.83 93.00 110.83 3.44
22.5 1.5 98.47 96.08 110.02 13.8910.0 1.5 96.94 165.02 110.84 5.66
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A.T.U. And amplifier stressesA.T.U. And amplifier stresses
A)ZL=50-J62.5Eff=93.5% Po=4.5W Ip=15.5A
B) ZL=50+J62.5Eff=90.9% Po=2.02W Ip=1A
C) ZL=19.5+J24.4Eff=84% Po=44W Ip=105A
D)ZL=19.5+J24.4Eff=93.8% Po=395W Ip=73.7A
90°
20°+20°
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Class D waveformsClass D waveformsRo=15 VSWR=1:1
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Class D waveformsClass D waveformsRo=15-j6.1 VSWR=1:1.5
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Class D waveformsClass D waveformsRo=15+j6.1 VSWR=1:1.5
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Class D waveformsClass D waveforms
Ro=22.5 VSWR=1:1.5
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Class D waveformsClass D waveformsRo=10.0 VSWR=1:1.5
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Atmospheric dischargesAtmospheric discharges
• At the antenna
• In A.C.lines
• In telephone lines
Characteristics
Imax: 200 kA Itypical: 10 a 20 kA
dI/dT typical: 10 kA/useg
Risetime: 2 useg Decay time:40 useg to 50%
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Criteria to minimize damagesCriteria to minimize damages
• Disipators– Avoid charge acumulation using sharp points – or active systems
• Well designed grounding system– Low impedance direct paths– High impedance undesired paths– Radial equipotential conections– Antenna and ground conection closely located at
TX
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Discharge probability functionDischarge probability function
N = 15 L (C·H+h)2 ·10-6
N = Discharges per yearL = Ceraunic level (Nº of days per year when thunderstorms are heared) C = Site topographic index (0 to 0,3)H = Site mean heigth above surroundings (1 to2 km)h = Antenna heigth
Example: C=0.1 L=50 H=100m h=120mN = 12.7 discharges per year.
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Discharge current Discharge current circulationcirculation
1
14
10
7
2
5
3
8 6
11
4
13 1215 9
16
17
1. Strike 2. Antenna 3. Discharge through the antenna 4. Guy 5. Isolator 6. Spark gap 7. Ground rod 8. Base insulator 9. Cnecting Loop11. A.T.U. isolator12. A.T.U.13. Ferrite core14. Coaxial cable15. Discharge current in caxial cable16. A.T.U. Spark gap17. Disipator
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Equipment InstalationEquipment Instalation
A.C. Line transient protector
Panelboard
Coaxial cable
Building ground
Ferrite toroids
Transmitter A.C. line
A.C. mains
Reference ground
Ground to auxiliary
equipment
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Ground system equivalent circuitGround system equivalent circuit
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Discharge voltages and currentsDischarge voltages and currents
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InterferenceInterference
1.- Intermodulation products are generated
2.- SWR protection is desensitized
3.- Dangerous voltages at the R.F. Amplifier and output filter maybe generated.
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Transmitter ProtectionsTransmitter Protections
•A.C.inputOverloadShort cicuitTransientsOvervoltageUndervoltageAssimetry
•D.C.supplyOverloadTransientsFailure
• R.F.OvercurrentSWRPhaseoverpowerTransients
• Internal R.F. Drive TemperaturePLL
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Factory tests to ensure transmitter Factory tests to ensure transmitter reliabilityreliability
• Power amplifiers– Long time operation at 150% modulation
• Output– Open cicuit– Short circuit– Simulated lightning strike– SWR
• A.C. input– Phase failure– Simulated transient– Voltage variationSENDER
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ConclusionsConclusions
• Transmitter intrinsic reliability– Power stages regimes much lower than devices
limits– Simple low power stages with low number of
components
• Rational protections adjustment
Reliability in a transmitting sytem is a function of:
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ConclusionsConclusions
• High quality station engineering– A.C. Transient protection– Antenna discharges protection– Well dimentioned and coordinated grounds.– Stable radiating sysytem.– Interference filtering
• Coordination with the manufacturer
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Recomended instrumentation for Recomended instrumentation for test and adjustmenttest and adjustment
1.- To measure resonance:1.1 R.F.Generator
1.2 Oscilloscope or spectrum analyzer
2.- To measure R.F.impedance:2.1 R.F. bridge (General Radio 1609 or Delta OIB-3)2.2 R.F. generator (Delta RG3-A or similar)2.2 Spectrum analyzer (HP 8553B or similar) or detector included in RG3-A
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3.- To measure power:3.1 R.F. Dummy load,non inductive or with
a tuning network to adjust it to 50+J0 Ohm.3.2 R.F. Ammeter (Delta TC-1 or similar)
or R.F. Wattmeter
4.- To measure frequency response and distortion:4.1 General purpose oscilloscope, 2 channel 4.2 Audio analyzer (Audio precision Portable
One or similar)4.3 Modulation monitor (H.P. 8901 A or B , Belar
AMM3, TFT 923 A.M. or similar.)
2.3 An H.P. vector impedance meter may be used instead of 2.1,2.2 and 2.3
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5.- To measure spectrum.-5.1 Spectrum analyzer 100KHZ.to 50 MHZ or more
TEK 2711, H.P. 8553B plus display unit or similar).5.2 R.F. atenuator.5.3 OPTIONAL. Notch filter to remove the carrier
frequency and avoid intermodulation
6.- To check efficiency.6.1 A.C. Analyzer.(To measure A.C. voltage, current,
power and power factor
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7.- To measure transmitter carrier frequency. 7.1 Digital frequency meter up to 10 MHZ. Or higher frequency, time base 1 P.P.M. or less.
8.- To measure temperature.8.1 Infrared temperature measuring unit with suitable digital multitester. (Fluke).
9.- For general voltage and current measurements:9.1 True RMS digital multimeter, suitable to operate in high R.F. fields. (Our best experience is with Fuke Digital multimeters.)
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10.- For long run test.10.1 USASI Noise generator. (Delta SNG-1).
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SENDERSENDER
Pablo Phillips D.
Agosto 1999
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