VHF_COM

1.Introduction

Receiving information from FM mete-orological satellites has become an inter-esting hobby for thousands of radioenthusiasts all over the world. Those ofyou who have already tried internetsearches using such keywords as NOAA,METEOSAT, 137.5MHz, WEFAX , Me-teor etc. , will undoubtedly confirm thatthey have found hundreds of links topages of receiver manufacturers, re-sel-lers, professional users and particularlyham enthusiasts.You will find among others, a link to thehomepage of Radek Václavík OK2XDX,which is devoted to these issues [1]. Hisarticle on a downconverter for Meteosatreception was published also in the VHFCommunications issue 4/1999 [28,29].It is worth noting that on 1st April 2000we commemorated the 40th anniversaryof the first transmission of images fromthe satellite TIROS 1. The pictures wereof rather low quality, nevertheless, theystarted an era of space research of theEarth’s surface. The resolving power oftodays images is currently of the order 1pixel = 1 m. You can find more detailedinformation on the internet pages of theNOAA agency http://www.earth.na-sa.gov/history/tiros/tiros.html.

Quite and few hams tried successfully inthe seventies to construct receivers.These obviously did not have the techni-cal specification that can be achievedwith modern components. Images werenot generated using high quality decod-ing programs for personal computers,simply because they did not exist at thattime. The images were “decoded” usingof technology of the seventies; plottingon oscilloscope with medium afterglowand then photographing using an instantPolaroid camera [9].

2.Looking at earth from space

Satellites NOAA (USA - National Ocea-nographic and Atmospheric Administra-tion) and METEOR, OKEAN, RESURS(Russia) are the focus in this article.They are flying on polar orbits aroundthe Earth at the distance of approxi-mately 800 - 1200 kilometres passingover the same place at approximatelysame time every day [23]. Satellites passthe North or South pole on each orbit,that is why their orbits are called polar. Itis possible to determine their trajectoryprecisely using “Keplerian elements”,which describe the current orbit of thegiven satellite. Calculation of the exacttime of a satellites orbit, from the mo-

Miroslav Gola, OK2UGS

FM Receiver For 137 - 141MHz(A double conversionsuperhetrodyne with pll)

VHF COMMUNICATIONS 3/2002

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ment when it appears at the horizon tillthe moment when it disappears behindthe horizon, can be made nowadaysusing many programs for personal com-puters. I most frequently use a simpleWindows program called SatWin [10,24]. A version of SatWin was alsowritten for MS-DOS and can be run onolder personal computers of the DX486type. Both these programs can be down-loaded free of charge together with up-to-date Keplerian elements at the follow-ing address: http://www.emgola.cz/. Youwill also find other information about theactivities of satellites plus the signals thatyou can receive and decode using thereceiver described in the following arti-cle. Pictures are transmitted continuouslyfrom polar satellites without beginning orending. When the satellite appears overthe horizon, the edge of the pictures isslightly cramped, gradually resolution ofdetails in the picture improves. At theend of orbit the signal gets weaker andthe picture begins to disappear in noiseas the satellite slips behind the skyline.Inclination is the angle made by the planeof satellites orbit and equatorial plane. Asatellite that passes over both poles (onso called polar orbit) has the inclinationof 90°. The inclination of Americansatellites NOAA 10-16 is 98°, their pe-riod is approximately 102 minutes andheight of satellite is approximately 820 -850 kilometres.Signals from the satellites are in WEFAXformat (Weather Faximile). This is anold, but still useful, system for transmis-sion of black and white visual informa-tion using a standard audio channelwhere a change of amplitude of the2400Hz sub carrier represents the levelof the video signal brightness. Maximummodulation (black) is not zero, but ap-proximately 5%, white is then approxi-mately 87%. This audio signal is fre-quency modulated on the main carrier,e.g. 137.50MHz for the satellite NOAA15. After demodulation by the FM re-ceiver we therefore obtain an amplitudemodulated tone of 2400Hz. This signal is

sent to the input of standard sound cardin a PC and processed by a softwaredecoder such as JVComm32 which canbe downloaded from http://www.jvcom-m.de/. JVComm32 even handles badquality demodulated signals due to theefficient digital filters. The result of thisprocessing is shown in Fig 12 as picturedisplayed on a computer monitor.Transmission of images from NOAAsatellites are composed of lines lasting0.5 second, which correspond with datafrom sensors. They provide one pictureof the Earth surface containing data fromtwo channels. Channel A transmits pic-ture in the visible spectrum (VIS) andchannel B transmits picture in the infra-red spectrum (IR). Each line containstime multiplexed data from both channelsand is composed of separation tonesinterlaced with picture modulation. Datafrom channel A is preceded by and shortimpulse of 1040Hz and similarly datafrom channel B are preceded by andshort impulse of 832Hz. Each line alsocontains a calibration sequence. Thanksto this the decoding program can displayonly the chosen type of picture. You willfind more detailed information at http://www.noaa.gov/. You will find up-to-dateinformation about Russian satellites ME-TEOR, OKEAN, RESURS at http://sput-nik.infospace.ru/. These satellites havehigher orbit than that of NOAA satellites(1200 km). For example inclination ofsatellites METEOR is 82° and their pe-riod is 115 min. The system of picturetransmission from METEOR satellites iscompatible, however slightly different,from that of NOAA satellites. Modula-tion is similar, but pictures contain onlyone photo with higher resolution. Edgesof lines contain sets of phasing lines(alternately black and white), the linesmark end of picture and greyscale. Pic-tures in the infrared spectrum do notcontain the greyscale. The pictures arealso inverted as in comparison withNOAA pictures. Photos from NOAAsatellites show warmer places by darkershade and colder places are brighter. The


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pictures from METEOR use inverse scalewarm seas are white and cold cloudformations are black.It is also possible to decode visual infor-mation from the receiver any time. To dothis it is necessary to save the receivedmodulated signal as a WAV sound fileon a high quality recorder (we had thebest results with SONY Minidisk). If youtake holidays in distant countries, it isrecommended that you use a portable andeasily mounted Quadrifillar Helix an-tenna, see [19], take the receiver de-scribed below and a Minidisk. Duringyour trip you can record exotic picturesfrom any of the meteorological satellites.When you return you can decode thesaved WAV sound files in the samemanner as during direct reception.

3.Description of the receiverRX-137-141MHz

The receiver RX-137-141MHz has beendesigned for high quality reception ofsignals form polar meteo-satellitesNOAA, METEOR, OKEAN and others.It is compatible with the converter from1691MHz to 137.50MHz which is suit-able for reception from geo-stationarysatellite METEOSAT 7 [14, 23].Looking at the Table 1, you will find thatsatellites in polar orbits transmit signalsin the range of 137.30-137.85MHz,therefore a very narrow frequency rangeis sufficient. We have chosen, for practi-cal reasons, a lower frequency of137.00MHz and an upper frequency of141MHz. No meteorological satellitest r ansmi t a t f r equenc ies above137.85MHz but the frequency of

NOAA 11 137.62MHz Not operatingNOAA 12 137.50MHzNOAA 13 137.62MHzNOAA 14 137.62MHzNOAA 15 137.50MHzNOAA 16 137.62MHz Not operatingNOAA 17 137.62MHzNOAA beacons 136.77 and 137.77MHzMETEOR 2-21 137.40MHzMETEOR 3-5 137.30MHzOKEAN-O 137.40MHzRESURS O 1.1 137.85MHz

Table 1 : Not all the satellites given are always active. Some of them are stillflying on polar orbits, but their transmitters have been switched off. Someothers do not transmit due to a failure, e.g. the modern satellite NOAA 16 onlytransmits in the mode HRPT at the frequency 1.698 GHz due to a defect. This isthe fate of all artificial satellites, when they fail they can only be repaired usingvery costly methods. Not all the satellites are as important as the Hubble spacetelescope, which was repaired by the space shuttle that we watched withexcitement and admiration.See http://noaasis.noaa.gov/NOAASIS/ml/status.html


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141MHz will make it possible to use theconverter for the METEOSAT 7 satellite.This makes it possible to process infor-mation from both channels, the firstchannel (1691MHz) converts to137.50MHz and the second channel(1694.50MHz) converts to 141.00 MHz.The circuit diagram of the receiver isshown in Fig 1. It was originally devel-oped for the nearby ham frequency rangeof 144-146MHz [3]. The circuit of thereceiver is designed for wideband FM(bandwidth 30kHz). The low-frequencyWEEFAX signal is sent from the outputto the PC sound card. The frequencysynthesiser PLL and LCD display arecontrolled by an ATMEL micro-com-puter.The receiver is a double conversionsuperhetrodyne. Design of the receiverhas been significantly simplified by usingan MC 3362P (IC1) integrated circuitmade by Motorola [5], which comprisesall main elements of modern FM re-ceiver. All that is required to connect tothe MC3362P is an input band-passfilter, a resonant circuit for the first mixeroscillator, 2 ceramic filters for 10.7MHzand 455kHz, a quartz crystal oscillatorfor the second mixer, a resonant circuitfor the demodulator and few other pas-sive components. We will thus obtain anexcellent receiver with a rather simplecircuit and with supply voltage of 2-5V[12].

3.1 Input circuits of the receiverThe signal from the antenna (or from the

converter) go to a capacitance dividerC2-C3 (input impedance adjustment).The divider together with L1 forms thefirst tuned circuit, the “hot end” of whichis connected to T1 a dual gate MOS-FET, preferably “low-noise” type BF982.T1 ensures sufficient amplification of theinput signal. Resistor R3 suppresses thetendency of input amplifier to oscillate,but it does reduce overall amplification.The signal from resistor R3 is furtherfiltered by a band-pass filter L2-C5,L3-C8, L4-C11+C12 with the bandwidthof approximately 4MHz. Critical cou-pling between the band-pass filter cir-cuits is determined by serial connectionof SMD capacitors C6 + C7 and C9 +C10. The signal passes through the ca-pacitance divider C11+ C12 to the inputof the first mixer in IC1 with mixingsignal from oscillator (L5, C33).

3.2 PLL OscillatorThe stability of the oscillator for the firstmixer is achieved using a PLL withreference frequency of 4MHz. IC4 is aPhilips SAA1057 single chip synthesiserdesigned for tuning of VHF FM radioreceivers with medium frequency band-widths [4, 6]. It was produced in 1983,but surprisingly enough it is still avail-able on the market and at very goodprice. In the circuit shown in Fig 1 thesynthesiser can be tuned from 110MHzto 150MHz with steps of 10kHz using amaximum tuning voltage of 4.5V. Thetuning voltage (max. 5.5V) is taken fromthe power supply to the pin 7 of IC4.R14, C25 and C26 are the passive com-

Frequency range: 137 - 141MHz, smoothly in steps of 10kHzFunction SCAN: 137.00 137.30 137.40-137.50 137.62 137.85-141.00MHz,Intermediate frequencies:10.7MHz and 455 kHzInput sensitivity: 0.4µV (rms-typ.) for 12dB SINADOutput signal: 2400Hz amplitude modulated (black 5% and white 87%)Display: LCD single line, 16 displayed charactersCurrent consumption: 70mA, (with converter LNC1700 250-500mA)

Table 2 : Specification of the receiver.


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ponents of the phase detector, C27 filtersthe internal stabilised voltage. The stabil-ity of the PLL is determined by the filterconnected to pins 5 and 6 of IC4, R15,R16, C28, C31, C56, C57 determine thetime constant of active low-pass filter. Itis important here to pay special attentionto recommended values of components.The tuning voltage from the PLL isconnected to the pin 23 of IC1 to aninternal varicap diode. The output fromthe first oscillator of the circuit in IC1(oscillator buffer) is connected throughthe coupling capacitor C35 to pin 8(FFM), the input pre-divider of the syn-thesiser IC4. In the majority of applica-tions of the SAA1057 the referencefrequency is determined by a 4MHzinternal oscillator controlled by externalquartz crystal connected to pin 17 (X). Inour circuit we have chosen an economicoption and used a common quartz crystalfor the reference frequency of both PLLand ATMEL micro-computer [7]. Thequartz crystal X1 is part of the oscillatorin IC3 and the reference frequency forIC4 is connected through the capacitorC24 and resistor R11.For the first mixer we have chosenfrequency one intermediate frequency(10.7MHz) lower than the signal fre-quency. The synthesiser therefore gener-ates frequencies from 126.3MHz to130.3MHz for a reception frequencyrange from 137.0MHz to 141MHz. Thesynthesiser frequency can be finely tunedwith use of trimming capacitor C21. Thecontrol word for setting the dividing ratioof the divider is accepted by the synthe-siser IC4 through the inputs CLB,DLEN, DATA from the micro-processorIC3 via a three wire data bus, C-BUS,which is also connected to the connectorPC-BUS for other uses.

3.3 Intermediate frequencyThe first mixer oscillator is 10.7MHzlower than the input signal. The differ-ence component (fIN-fOSC) is the inter-mediate frequency signal of 10.7MHzbeing amplified by the amplifier in IC1

and fed to the ceramic filter F1, this is acommon type muRata 10.7MHz/180kHz. The filtered signal is fed to thesecond mixer where it is mixed with thesignal of a quartz crystal oscillator withthe frequency of 10.245MHz (X2). Theresulting difference component is filteredby ceramic filter 455kHz (F2) with abandwidth is 30kHz. Due to frequencyswing of the WEFAX signal’s modula-tion of +/-17kHz the width of F2 shouldbe approximately 40-50kHz. Unfortu-nately, the only ceramic filter available isthe muRata/455/B. We have found thatthe narrower width of the filter has anunrecognisable impact on quality of thefinal image. Modulation of the first oscil-lator can have a substantial influence onthe quality of decoded image. That iswhy increased attention must be paid, inthis project, to the feedback loop of thePLL.The signal after the filter F2 is amplifiedin the internal limiter with the output tothe quadrature demodulator, which usesthe resonance circuit L6-C19. In order toensure only minor signal distortion afterdemodulation the linear characteristic ofthe demodulator must have width of atleast 40kHz. For this reason we havechosen the value of the damping resistorof 39k. For use with the METEOSATsatellite a bandwidth of approximately20kHz is sufficient.

3.4 Low-Frequency outputThe demodulated low-frequency signal isa tone of 2.4kHz that passes through asimple filter, formed by R19, C37, C38,which suppresses undesirable products.After the filter the signal is divided intotwo parts, one to the potentiometer P2which feeds the low-frequency amplifierIC2 with output to the loudspeaker, theother to the pre-amplifier IC6 for the2.4kHz tone decoder circuit IC7, and alsoto the output for the PC sound card.

3.5 2400Hz tone decoderA tone decoder [13] was included in thereceiver after considering possible modi-


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fications to the software for the originalreceiver from [2, 3, 8]. From the table oforbit times for individual satellites andfrequencies at which they transmit, it isapparent that the receiver must scan theband from 137 - 141MHz and stop onlyat signals with modulation by a tone of2400Hz and not at incidental interfer-ence. We have chosen a simple algo-rithm; the receiver performs a test afterswitching on and stops at the first chan-nel having a signal modulated by tone of2400Hz. When the satellite disappearsbehind the horizon the signal modulatedby a tone gets lost in the noise and thereceiver begins scanning again. It stopsat the next signal with 2400Hz tonemodulation. The tone decoding is reli-ably accomplished by the integrated cir-cuit NE(SE)567 (IC7). As soon as asignal appears on the input of the tonedecoder, it is compared with the fre-quency of the internal oscillator. When atone is detected the output, pin 8, of IC7is set to the a low level and diode D1 islit. The frequency of internal oscillator isset roughly by the capacitor C55 andaccurately to the value of 2400Hz by thetrimming resistor R25. The logic signalon pin 8 of IC7 is connected via thejumper JP3 to the input of the microproc-essor SQ OUT which controls mode ofautomatic searching for signals in thereceived bandwidth (SCAN). The jumperJP3 can be used to select control ofautomatic scanning for signals either onthe basis of presence of 2400Hz tone, orby active squelch.

3.6 SquelchA side effect of receiving weak FMsignals or operation of the receiver be-yond the tuned station is an unpleasantnoise in loudspeaker. That is whysquelch (SQL) forms an integral part ofany FM receiver. It interrupts the low-frequency signal to the amplifier at ab-sence of sufficient level of input signal.The DC component of LF signal from thepin 10 (MetDriv) of IC1 is fed throughR4 to the potentiometer P1, which is

used to set the sensitivity threshold of thesquelch. When the slider of potentiom-eter P1 is in the extreme left position thesquelch is disabled. Turning the potenti-ometer clockwise increases the level atwhich the squelch switches off. Pin 11 ofIC1 is carrier detect which is used tocontrol the squelch switch having a volt-age of approximately 0V for a signalwithout noise or a voltage of approxi-mately 2.8V for no signal, or a signalwith increased noise level. This is in-verted by transistor T2 and fed to pin 8of the loudspeaker amplifier IC2 thatmutes the signal path when the squelch isactiveWhen the squelch is switched off thecollector of the transistor T2 and pin 8 ofIC2 have voltage of 1.25V, and thelow-frequency is not muted. When atconstant signal is received at the antennaand the potentiometer P1 is turned clock-wise, we will reach a state where thesquelch activated i.e. a voltage 0V ap-pears at the collector T2 and the low-frequency path is muted. When signalvoltage on the receivers input increasesslightly the squelch deactivates andopens the low-frequency path.The squelch signal has been used also forautomatic scanning of signals. We haveadded transistor T3, which inverts thesquelch signal which can be connected tothe input P3.0 (SQ OUT) of the micro-processor IC3. The processor programthen takes care of the rest (see thechapter Setting-Up Of The Receiver formore details).Note: If you do not like the smallhysteresis of squelch, connect pins 10and 11 of IC1 using a resistor of 2 - 5M(R30) and connect a ceramic 100nFcapacitor (C61, preferably SMD) be-tween pin 11 and GND. Another optionto soften the squelch rise time is to use anelectrolytic capacitor C60.


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4.Experiment with an AFCcircuit

During the design of this receiver de-scribed in [2, 3, 8] experiments weremade for AFC. This tuned the frequencyof the reference oscillator using the DCcomponent of the voltage from the quad-rature demodulator at pin 13 of the IC1.This was connected to the inverting inputof an operational amplifier TL071 withit’s output connected to a pair of varactordiodes, KB105G, which replaced thetrimming capacitor C21 in the circuit ofreference oscillator. Thanks to the verygood stability of PLL we did not noticeany change in quality of the final imagewhen AFC was used, that is why wedecided to exclude the AFC circuit inorder to make the design as simple aspossible. For people interested in AFC,the circuit diagram is available at theauthors homepage.In relation to the use of AFC, it isappropriate to mention Doppler shiftingof frequency. This phenomenon is ob-served if a signal source, in our case ameteorological satellite, is approaching,

you perceive it’s frequency as higher,and when it moves away, you perceiveits frequency as lower than it in fact is.The magnitude of the Doppler shift fororbital satellites is a maximum of 5kHzwhich is still in the pass-band of thefilters and does not cause visible distor-tion of final image.

5.Antenna

A requirement for assuring high qualityreception of signals from meteorologicalsatellites is the use of a high qualityantenna. Polar meteorological satellitesare rotation stabilised and transmit circu-lar polarisation. It is therefore impossibleto use ordinary Yagi or ground planeantenna. When you listen to the signalfrom the loudspeaker it seems to be noisefree, however when you observe thepicture after it is decoded you will seethat it is unusable. Anyone can build highquality antenna. Two basic types areused: Turnstile and Quadrifillar Helix.The turnstile consists of two crosseddipoles (Fig. 2) phased for circular po-larisation. This antenna should be situ-

Fig 2 : General viewof a Turnstileantenna.


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ated as high as possible above the hori-zon, preferably above the house roof orin an open air space. Experiments madewith a turnstile antenna located on thebalcony of a blockhouse, satellites flyingover at a low elevation angle wereshielded by building or balcony. In short,

it is only possible to receive signals thatare “seen” by the antenna. Instructionsfor building several types of turnstileantennas are on the authors homepage.Drawings describing the construction ofa simple antenna made from plastic tubeand 8 - 12 mm aluminium tube are givenin the literature [18].We have tested the antenna shown in Fig3 with the receiver. The antenna wasinstalled on a roof at 40m above theground and gives high quality signalreception. The feeder connection for cir-cular polarisation is shown in Fig 4. Fig5 shows the polar diagram for this an-tenna, particular attention should be paidto the dipole to refelctor spacing becauseit changes the polar diagram, the authorchose 3/8λ.The manufacture of the Quadrifillar He-lix antenna, which is shown in Fig. 6 canbe done only in a well equipped machineshop. This antenna has slightly betterreception of signals and moreover it canbe used also in moving objects, such asyachts cruising in Mediterranean Sea.The article [20, 21] contain many de-scriptions of simpler mechanical con-structions suitable, however, only for ashort-term seasonal use, or for antennasmade of copper heating tubes. If thedistance of your receiver from the an-tenna will exceed 10m, I would recom-

Fig 3: Practical design of a turnstileantenna.

Fig 4: Detailsof feeder forturnstileantenna.


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mend use of selective pre-amplifier forfrequency range of 137MHz, preferablyusing bipolar transistor. Experience hasshown that summer storms have a ratherbad impact on MOS-FET transistors. Inan environment with industrial interfer-ence it is often desirable to use a bandpass helix filter in front of the pre-amplifier.

6.Power supply for the receiver

The receiver requires a stabilised powersupply adapter with a voltage of 9 - 12V.It is highly that you pay special attentionto the selection of a power supplyadapter. If you have an oscilloscope, lookat it’s output when on load at 150mA andcheck that there is no ripple. The low-frequency amplifiers IC2 and IC6 are feddirectly from the adapter. The othersupply voltages, 5V for receivers circuitsand 5V for synthesiser and microproces-sor, are stabilised by IC5 (LM7805). Thesupply voltage for the analogue part ofthe receiver is also isolated by choke L6.The input of the power supply is pro-tected against reverse polarity by diodeD2. Bridging jumper JP2 enables the usethe feeder cable to supply the antennapre-amplifier or Meteosat converter. Thisrequires a higher capacity power supply

adapter, for connection of the OK2XDXMeteosat converter [16], I recommend apower supply adapter of 12V/500mA.

7.Construction of the receiver

Building the receiver is very simple, itcan be done by any beginner, who has aknowledge of rf techniques, and is ableto use a multimeter. If care is taken therewill be no need for special rf measure-ment equipment. The secret of success isto put the correct value components inthe right place on the printed circuitboard and solder them in properly.If you build the receiver from the EMGOkit you will have all of the components

Fig 6 : General views of QuadrifillarHelix antennas.

Fig 5: Polar diagram for turnstileantenna.


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needed. First of all visually check thecomponents against the parts list. Thevalues of the resistors and capacitors canbe checked, the resistors can be measuredand the markings checked on the capaci-tors. Do not forget that the marking 470on some capacitors does not mean470pF, but 47pF. It is important that youpay special attention to this initial meas-urement of components and visual in-spection, including printed circuits. Afterfirst construction guide was published [3]I agreed, out of curiosity, to completeseveral almost finished kits. Althoughthese receivers seemed to be assembled,they did not work. In all the cases I foundthat this was caused either by mistakes,negligence or bad soldering of compo-nents. After minor repairs all of thereceivers worked perfectly.After visual inspection of the printedcircuit board (PCB) fit the four pillars inthe corners, they will simplify the inser-tion of components (Fig 7). Start byfitting the 9 SMD capacitors and oneSMD resistor using a small quantity of1mm diameter SnPbCu solder. Next in-sert and solder the remaining resistors,capacitors, semiconductors and the con-nectors for the loudspeaker and powersupply starting with small componentsand continue with larger ones. Socketsare used for the integrated circuits IC3and IC4. Before soldering the two quartzcrystals, X1 and X2, fit a 0.5mm paperpad and removed it after soldering. Simi-larly the 5 TOKO coils with metal coversshould be fitted into PCB with smallspace of about 0.5 mm., this prevents thecase shorting to other tracks on the PCB.The tank circuit of the discriminator, L6,also has a metal cover and should befitted approximately 0.5mm above thePCB. If L6 does not contain a capacitor,fit C19. Finally fit the switch SW1 andJP3 and connectors LINESB and LIN-EREP. If you use your own printedcircuit board and it does not have platedthrough holes, do not forget to solder thetop and bottom of components leads andfit fed through wires where required. Fit

the pre wound coils L1 to L5 for theinput band-pass filter, these are highquality coils made by Japanese manufac-turer TOKO.If you manufacture the coils yourself,you must wind 2.75 turns of 0.215mmenamelled copper wire on 5mm formers.Solder the wire ends to the metal pins onthe bottom of the former and cover thecoil with a droplet of beeswax. Turns onall the coils must go in the same direction(e.g. clockwise). Insert the coils to thePCB and check orientation before solder-ing. Put a metal cover over the formerapproximately 0.5 mm above the printedcircuit board. Finally fit ferrite coresmade of N01 (150MHz) into the formers.The following components will be fittedduring set-up using rf measuring equip-ment: capacitors C11, C12, ceramic fil-ters F1 and F2, integrated circuits IC1(microprocessor AT89C2051 with theprogram RX137DIP4X ) and IC4 (PLLSAA1057). If you do not have rf measur-ing equipment, insert all the componentsin accordance with the component lay-out.Fit the components onto the front panel(Fig 10) including the support plate forthe LCD display and its fixings to thereceivers main PCB. First fit the buttonsTL1 and TL2 to the panel from the frontand the 100k trimming resistor, for set-ting of display contrast, to the panel fromthe back. If you use a back lit LCDdisplay, you must also fit the 120Ωlimiting resistor. The panel will be fas-tened to the receivers PCB by solderingat the bottom corners, at places without aprotecting layer of solder mask. This isstrengthened by installation of two thepotentiometers P1 and P2, and the angu-lar connector. After checking that thepanel is perpendicular to the receiversPCB you can solder all terminals ofpotentiometers and angular connector.Insert the 16 pin connector into the toppart of the panel from the front andsolder it from the back. Finally insert theLCD display form the front and solder its


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16 pins to the front panel. Secure thepotentiometers P1 and P2 by fitting theshaft nuts.After putting the receiver RX-137-141into operation you can fit it into asuitable plastic or metal box with aper-tures for the display and controls. Theantenna and power supply connectors areat the rear of the box. Fig 13 shows thereceiver mounted in a suitable box.

8.Setting-up of the receiver

Connect a stabilised power supply, of 9 -12V, to the input connector U12. Ensure

the centre connector is positive and theouter is ground. Using a voltmeter meas-ure +5V at the stabilised output of IC5.If there are problems with the noiseproperties of the receiver, check thestabilised voltage using an oscilloscope.If there is noise on the supply thestabiliser must be replaced.The procedure for commissioning andtuning of the rf components will dependon the instruments available to the indi-vidual constructors [22]. The receiversboard is already fitted with all compo-nents except the intermediate frequencyfilters F1 and F2. Do not fit the micro-computer IC3 and synthesiser IC4 intotheir sockets. Turn the potentiometer P1(SQL) completely to the left, this will putthe squelch out of operation. Do not

Fig 7 : Componet layout of the main receiver PCB.


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Fig 8 : Top side of the main receiver PCB.

Fig 9 : Bottom side of the main receiver PCB.


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connect the shorting pin on the switchJP3. For tuning L1 - L4 at the receiversinput and the demodulation discriminatorL6 it is best to use a wobbler. Almostsame result can be achieved using an rfgenerator (even an improvised test oscil-lator 137 - 141MHz with one transistor)a counter and a simple rf diode probeconnected to an analogue voltmeter.Connect a signal with frequency of455kHz, preferably frequency modulatedby tone of 1kHz, with frequency swingof 30kHz to pin 7 of IC1 using a 1nFcapacitor. Connect an oscilloscope to pin13 of IC1 and tune L6 for maximumamplitude of demodulated signal. Byadjusting the value of R6 (a lower valuewill broaden the linear part of the curve)at least 30kHz of linear demodulationcan be achieved. If a signal generatorwithout frequency modulation is used,adjust it in steps 1kHz and plot a graphof the voltage at pin 13 of IC1. It is alsopossible to determine the value of R6experimentally by monitoring the imagequality (minimum noise, the highestloudness, sharpness of image details,etc.). The recommended value of R6 is33-56K.The next step is to fit filter F2 andconnect the output signal from a wobblergenerator or analyser to the receiversantenna input, connect the wobbler to pin19 of IC1. This will enable the inputselectivity to be adjusted without beingaffected by capacity of the signal source.Shunt the input coil L1 using a 50Ω

resistor and tune the band-pass filter L2,L3 and L4 to approximately the centre ofthe band (139MHz) and set the width ofband-pass to 4MHz. If you do not intendto use the METEOSAT converter withyour receiver, set the input band-passfilter to centre at approximately137.6MHz. If it is necessary modify C6,C7 and C9, C10 (0.5-1pF) in order toadjust the coupling of the resonant cir-cuits to critical or slightly supercritical.Remove the shunt resistor from L1 andalso tune it to the centre of the selectedreceived band, i.e. to 139 or 135.6MHz.Now fit filter F1 and to insert thesynthesiser and microcomputer ICs intotheir sockets. Switch on receivers powersupply and use the trimming resistor onthe front panel to set the LCD displaycontrast so that characters are legible. Ifturning of trimming resistor to both ex-tremes does not help and no charactersappear on LCD display, use an oscillo-scope to check communication betweenPLL IC4 and microprocessor IC3 (pins 8(CLB), 9 (DLEN) and 11 (DATA) TTLlevels). Push any button on the displaypanel and look for a sequence of im-pulses, when microprocessor sends newdata to the PLL synthesiser. If this isunsuccessful, check that the microproc-essors reference oscillator is working.With the LCD display showing a fre-quency of 137.5MHz, connect a voltme-ter to the pin 23 of IC1 or even better tothe test point “UL” and check that thefirst oscillator PLL is functioning cor-

Fig 10 : Component layout of the display PCB.


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rectly. Start by adjusting the core of L5using a non-metallic screwdriver andwatching the voltmeter for changes in thecontrol voltage of the PLL. The meas-ured voltage should not remain fixed at

either extreme, i.e. 0.2V or 4.3V. If thePLL is working, the tuning voltageshould vary smoothly between 0.2V and4.2V as the position of the core in L5 ischanged.

Fig 13 :Completedreceiver in aplastic case.

Fig 12 : Bottom side of the display PCB.

Fig 11 : Top side of the display PCB.


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If you have wound your own coil L5,you may have to adjust the value of C33.If the tuning voltage reaches the maxi-mum of 4.2V with the core almostunscrewed (minimum inductance), re-duce the value of C33 by one step. If thetuning voltage reaches the minimum of0.2V with the core completely screwedin (maximum inductance), increase thevalue of C33 by one step. In order toavoid such problems we recommend theuse of the specified TOKO coil.For example, for a received frequency137.50MHz - satellite NOAA 15 (oscilla-tor of the receiver oscillates at126.80MHz) set the voltage at the junc-tion of R16, C31 to approximately 2.5Vby adjusting the core of the L5. Checkthe exact frequency of the oscillatorusing a counter and tune it by slightchanging the trimming capacitor C21.The majority of constructors will prob-ably not have a wobbler or rf signalgenerator at their disposal. Neverthelesseven the modest ham shack equippedwith just a probe, a multimeter and“common sense” it is possible to tune theinput circuits to the lowest possible noisein the output LF signal. You just have tomake a test Colpitts oscillator, working at137.5 MHz. If you do not have a suit-

able circuit, I will gladly send it to youtogether with a PCB. You can then tunethe resonance circuits, by the followingmethod, to a minimum noise in theoutput signal. It is not necessary to makedirect connection of test oscillator to thereceivers input. it is sufficient to insert acut wire into the antenna connector, apaper clip formed to an “L” shape will dothe job. Set SW1-DIP4 to 137.5MHz andtune the frequency of test oscillator tothis frequency, i.e. when the noise disap-pears from the receivers loudspeaker (orat least its intensity is considerably re-duced). By touching the coil of testoscillator you can introduce “frequencymodulation”. At pin 13 of IC1 you cansee the signal using an oscilloscope, orby listening to the loudspeaker. Firstadjust the core of L6 for the lowest noisein LF signal and the loudest volume.Then tune the input circuit, L1 - L4, andgradually shorten the improvised wireantenna (or move the test oscillatoraway) to give the lowest noise in low-frequency. Do not use a metal screw-driver, make a non-metallic screwdriverfrom a piece of hard wood (preferablybamboo), or from suitable plastic mate-rial.Note: set the squelch off using potenti-ometer P1 set to its minimum value.

Fig 14 : Picture ofthe completedreceiver.


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When this procedure is complete you canlisten for received signals and set thecorrect squelch level. The synthesiserPLL must be set up before the alternativetuning method is used.Connect a 137 - 138MHz turnstile an-tenna [17] to the receiver’s input and setthe frequency for the NOAA or ME-TEOR satellites by using either switchSW1-DIP4 or buttons TL1/TL2. Thesesatellites should soon appear, consult thecurrent orbit timetable to verify thetimes. The switch SW1-DIP4 serves assimple memory to store pre-set frequen-cies after switching on of the receiver.When all the switches are set to theposition OFF, the PLL tunes the oscilla-tor frequency to 126.80MHz, thus thereceived frequency is 137.500MHz (sat-ellite NOAA15). Set the required fre-quency for the receivers oscillator byswitching some of the four switches ofthe selector switch SW1-DIP4x to theposition ON. Table 3 shows the setting ofthe 4 switches, however all 16 combina-tions in binary code can been used.To commission of the low-frequency partof the receiver all that is required is to setthe gain of the amplifier for the loud-speaker and sound card using an oscillo-scope, or by just listening to the audiooutput. Set the amplification of IC2 tothe required value by adjusting R28(3R3=74dB, 10R=70dB, 33R=54dB,105R=44dB, 820R=34dB) with C59100uF. Set the tone decoder IC7 byadjusting R25 so that the LED diode D1lights up whenever a tone of 2400Hz isdetected in the received signal. The opti-mum input sensitivity of the decoder hasbeen chosen during development. Should

you have any reason to change it, choosedifferent ratio of resistors R22 and R23.The output from pin 8 is connected usinga jumper on JP3 to the input SQOUT ofmicrocomputer. SQOUT can also be con-nected to the collector of transistor T3,which has a logical value depending onthe setting of the squelch and on magni-tude of input signal.

8.1 The Receivers control functionWith a jumper on JP3 position 2-3(TON), after switching on the receiverwill perform a first test for the absence oflow logical level on SQOUT. The test isthen repeated and if a 2400Hz signalabove the set threshold level is detectedon any channel, the processor stops tun-ing. When the signal disappears i.e. whenthe satellite sinks behind horizon, the testre-starts and re-tunes until another signalis captured. Tuning can be interrupted bypressing the push button UP (TL1) orDOWN (TL2), the receiver is set to thefrequency according to the selectorswitch SW1-DIP4. It is then possible totune manually from 137 - 141MHz insteps of 10.0kHz. Simultaneous pressingand holding of both push buttons re-starts scanning again. The LCD displaywill show the current received frequencyin MHz. With a jumper on JP3 position1-2 (SQL), the squelch output is con-nected to the input of processor SQOUT.The scan function still operates but isnow controlled by the level of thesquelch, and not the presence of a2400Hz tone.

9.How to connect a LF output ofthe receiver to your personalcomputer

After demodulation the receiver’s low-frequency output is an amplitude modu-lated tone of 2400 Hz, which can be

Receive freq. Oscillator freq. Switch

K0 137.500MHz 126.800MHz all OFFK1 137.300MHz 126.600MHz SW1 ONK2 137.400MHz 126.700MHz SW2 ONK3 137.500MHz 126.800MHz SW3 ONK4 137.620MHz 126.920MHz SW4 ON

Table 3 : Switch settings forsynthesiser.


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processed by several methods. WEFAXsignals used to be processed on oldercomputers without a sound card usingJVFAX 7.1a. (operating system Micro-soft MS-DOS 3.0-6.22). For those whowould like to reminisce, you can studythis issue on the web [19]. You will finda description of simple method, whichconsists of converting the amplitudemodulation to frequency modulation. Themaximum change of brightness is thenexpressed by a change of frequency ofapproximately 1500 - 2300Hz. This sig-nal is connected to the computer’s serialport using a simple comparator (EasyIn-terface) and processed by JVFAX 7.1a.Thanks to the negligible price of obsolete

computers you can make a receiver anddecoder at minimum cost and have con-tinuous receiption of pictures form me-teo-satellites.Modern fast computers with sufficientlybig operation memory give us a possibil-ity to use the most advanced programs.The demodulated 2400Hz signal is con-nected directly to the input of sound card.

9.1 Program for decoding of WEFAXsignals using JVComm32Decoding of pictures by personal com-puters is supported by many modernprograms [26]. I have tested a demon-stration version of JVComm 32. This is

Fig 15 : JVComm32 in action.


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an elegant program without the need foran EasyInterface, just connect the low-frequency output of the receiver to theLINE input of your sound card. I finallybought a full licence for use of thisprogram [27]. This program can be,however, only be used on a powerful PCworking under Windows 95/W98/W2000/W-NT. The following paragraphdescribes reception of an image and itsdecoding by JVComm32 version 1.0 or1.1.In 1998 the German author of the JV-FAX, Eberhard Backeshoff, DK8JV (e-mail address: [email protected] andhomepage at http://www.jvcomm.de/)wrote JVComm32 for decoding of WE-FAX, FAKSIMILE SSTV and othermodern modes, he continues to enhanceit and extend it. The program requires acommon 16-bit sound cards with it’sLINE input connected to the low-fre-quency output of the receiver. A disad-vantage of this program is that it requiresat least a 75MHz Pentium PC with 16MBof memory, operating system Windows95, W98 or Windows NT 4.0 and highquality graphic card (High or True Col-our) with resolution at least 800 x 600pixels. JVComm32 on the other hand canwork at the background and allows si-multaneous processing of received im-ages (viewing, cropping, sending to yourfriends by e-mail, etc.). The author, nev-ertheless, recommends for multitaskingat least 90MHz Pentium and 32 MB ofmemory as a minimum.Connecting the receiver to the input ofcomputer sound card is very easy. Fromconnector LINESB of the receiver con-nect the low-frequency signal to theconnector LineIn or microphone input ofthe sound card. Fig15 shows JVComm32in action, when a map is received inbackground for, the pictures receivedfrom the satellite NOAA are loaded fromthe folder, Picture files, to the desktop:

9.2 Description of softwareConfiguration of the program for recep-

tion of satellites NOAA or METEOSATis very simple. Set the mode to NOAA orMETEOR, and the Interface type toSound Card. The help with this programis also very user friendly, you will findall the details of setting and operation.

10.Kits

The author has produced kits for hamsfor several years and therefore knowsvery well that successful completion of aproject is often hindered by tiny problem.No matter how good a verbal descriptionis, it’s information capability is alwaysmuch lower than visual and/or audioinformation. That is why kits are sup-plied with a CD containing completeinformation. Kits contain a set of printedcircuit boards and parts. Fully assembledand tuned modules are also available fora slightly higher price.You can get more detailed information atthe following contacts:[email protected] or [email protected] or http://www.emgola.cz/

11.Literature

[1] Ing. Radek Václavík OK2XDX,Pøíjímaè and interfejs WXSAT (pøíjemsnímkù z orbitálních meteosatelitù) [Re-ceiver and interface WXSAT (receipt ofimages from orbital meteorological satel-lites)]. A-Radio Praktická elektronika,series of articles in issues Nos. 2-6/1997.[ 2 ] G ü n t e r B o r c h e r t D F 5 F C ,Funkamateur 2/1995, str. 153 - 156 DerW e t t e r f r o s c h - e i n 1 3 7 M H zSatellitenempfänger, continuation inFunkamateur 3/1995, p. 274


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[3] OK2UGS.: Pøijímaè FM v pásmu144 - 146 MHz s obvodem MotorolaMC3362 [FM receiver for the band 144 -146 MHz with the circuit MotorolaMC3362]. A_Rádio_Electus99, pp.73-79[4] Maršík, V.: Kmitoètová syntéza os-cilátorového kmitoètu rozhlasovýchpøijímaèù [Frequency synthesis of oscil-lator frequency of radio receivers], Am-atérské Radio B3/1987, p. 88.[5] Motorola, Linear/Interface ICs De-vice Data, Vol.II, str. 8-82[6] Philips Semiconductors, SAA1057 -Radio tuning PLL frequency synthesiser,November 1983.[7] ATMEL, AT89C2051 8.bit Micro-controller with 1kbyte Flash, cataloguesheets August 1994.[8] DF2FQ: VHF Empfanger, CQ DL1/1994[9] Borovicka, Jiri, OK1BI. Personalconsultation history of receipts from theMeteosat, Antenna Turnstile[10] Our location database includes mosttowns and villages in the entire world(over 2 million places!) http://ww-w.heavens-above.com/[11] OZ1HEJ, Pedersen, Michael: Re-ceiver with LCD readout: http://ozon-.homepage.dk/eng/elcd.htm[12] OK2UGS.: Pøijímaè FM v pásmu144 - 146 MHz s obvodem MotorolaMC3362 [FM receiver for the band 44 -146 MHz with the circuit MotorolaMC3362.]. Elektroinzert 5/97 p. 6.[13] Philips Semiconductors: SE567 -Tone decoder/phase-locked loop, , 4/92[14] OK2XDX.: http://www.qsl.net/ok2xdx/[15] OK2UGS.: http://www.emgola.cz/Info.htm[16] Ing. Radek Václavik, OK2XDX:Prakticka elektronika No. 7/1999 con-struction guide to building of converterLNC1700 MHz

[17] L. B. Cebik, W4RNL: http://ww-w.cebik.com/turns.html The Turnstile AnOmni-Directional Horizontally PolarizedAntenna[18] Martin DH7GL: http://www.emgol-a.cz/Ant_GLdipol/GL_dipol.htm[19] Ruud JANSEN’S PA0ROJ: QFHAhttp://www.hshaarlem.nl/~ruud/ Skládacíanténa na cesty za poznáním [Foldawayantenna for exploration trips][20] Steve Blackmore: QFHA http://ww-w.pilotltd.net/qha.htm (step-by-step con-struction guide to building and QHFA)[21] Borre Ludvigsen: http://abdallah-.hiof.no/~borrel/QFH/ QFHA - More pic-tures and construction picture above isone of the designs on this site.[22] Josef Danes et al: Amatérskáradiotechnika and elektrotechnika, 3.èást , Mìøení na pøijímaèích [Hamradio and electrical engineering, 3rdpart, Measurement on receivers], pp. 190254, Naše vojsko, Praha 1988.[23] Gola, Miroslav: http://www.emgol-a.cz/jak_zacit_meteo.html[24] Kucirek, Petr: Program SatWinpøedpovìdi doby pøeletù satelitù nadzvoleným územím [Program SatWin pre-diction of time of passages of satellitesover the selected territory][25] Gola, Miroslav: http://www.emgol-a.cz/fapcsimile.html[26] Eberhard Backeshoff, DK8JV e-mail address: , homepage[27] Eberhard Backeshoff, DK8JV Whatdoes it cost and how can I get the fullregistered version?, http://www.jvcomm-.de/indexe.html[28] Vaclavik, R, OK2XDX: Easy down-converter for Meteosat, VHF Communi-cation 4/1999, page 196 - 207. http://www.vhfcomm.co.uk/[29] Vaclavik, R, OK2XDX: Small re-ceiver for Meteosat, VHF Communica-tion 4/1999, page 208 - 217. http://www.vhfcomm.co.uk/


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12.Parts list

Capacitors1pF 4 ceramic (SMD 0805) C6,C7,C9,C103p3 1 ceramic C25p6 1 ceramic C126p8 1 ceramic C310pF 1 ceramic C3312pF 3 ceramic C5,C8,C111.8 - 22pF 1 trimming capacitor CKT1 8-22pF

C2133pF 3 ceramic C22,C23,C2447pF 1 ceramic C1447pF 1 ceramic C19 (used if

not included in L6)150pF 1 ceramic C132n2 1 foil WIMA C254n7 1 foil WIMA C3710nF 1 ceramics C3510nF 2 foil WIMA C26,C4947nF 5 ceramic C4,C30,C32,

C36,C3947nF 1 foil WIMA C38100nF 9 ceramic C1,C15,C16,

C17,C18,C34,C43,C44,C47

220nF 1 foil WIMA C31330nF 1 foil WIMA C282M2/50V 1 radial electrolytic C2010M/50V 1 radial electrolytic C4547M/12V 2 radial electrolytic C27,C29100M/10V 1 radial electrolytic C46100M/15V 1 radial electrolytic C401000M/15V 1 radial electrolytic C48

Resistors and potentiometers2R2 1 R2047R 1 R3180R 1 R14120R 1 R10 (for LCD with back light)3k3 3 R8,R9,R114k7 2 R17,R1810k 4 R5,R7,R16,R1922k 1 R439k 1 R6 (39K - 56K see text.)47k 2 R12,R1350k/G pot 1 TP160, shaft 4mm P2100k/N pot 1 TP160, shaft 4mm P1100k 2 R1,R2100k trim 1 PIHER PT6VK100 P3 (setting of

contrast of LCD display)180k 1 R15

Transistors and diodesBF981 1 Dual gate MOS FET T1BC238 2 NPN universal TO92 T2,T3

Red LED 1 Any LED diode D11N4007 1 Rectifier diode 1A D2

Integrated circuitsMC3362 1 RX FM 2x MF IC1LM386 2 LF amplifier IC2,IC689C2051 1 With program RX137141DIP4LCD

IC3SAA1057 1 PLL up to 160MHz IC4LM7805 1 Stabiliser +5V IC5SE567 1 Tone decoder IC7LCD-DV-16100 Single line display LCD1

Coils7MC455kHz 1 TOKO 455kHz/600µH L6Choke 560nH-1 µH 2 axial, TLM20.1µH inductance 5 TOKO or 2.75 turns, see

text L1, L2, L3, L4, L5

OtherX-TAL 10.245MHz 1 Quartz X2X-TAL 4.000MHz 1 Quartz X1F 455 kHz/30kHz 1 Ceramic filter F210.7MHz 1 Ceramic filter F1Socket DIL8 1 low Pro IC2Socket DIL18 1 low Pro IC4Socket DIL20 1 low Pro IC3BNC connector 1 Antenna connector FSpacer 4 M3x5 mmNut M3 4 Fe/CdCon. SCD-016A 1 power supply socket

12V-2.5mmCon. SCP-2009C 1 power supply plug

12V-2.5mmCINCH SCJ-0363 1 GM Elektronic, REP

connector.Switch DIP 4x 1 GM Elektronic, DIP1

connector.Push butn. P-B1720 2 GM electronic, display

board TL1. TL2,Push butn. P-B1720 2 GM electronic, main PCB

TL1Knob 2 GM electronic, for 4mm

shaft for P1 and P2Pin S1G11W 1 GM Electronic, to connect

the base of the receiverto LCD display

Loudspeaker 1 Conrad ElectronicPCB1 DISPL 1 138 x 37mmPCB2 M-BOARD 1 138 x 88mm


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