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AMATEUR RADIO By GARRY CRATT, VK2YBX • The Dick Smith satellite receiver Recent developments in C band (4GHz) technology have led to the availability of affordable, low noise amplifiers suitable for the reception of satellite television signals. In fact, advances in receiver design have now been made to the point where international satellite television reception is within the reach of many enthusiasts. One company that has been involved in the development of satellite receiver design over the last few years is Dick Smith Electronics. They sell a complete 4GHz earth station for less than $7000. Lest readers are put off by such a sizeable price tag, we should mention that the major portion of the system cost is, naturally, the dish antenna which needs to be around 4 metres for reasonable results. However, amateur ingenuity being what it is, many enthusiasts are pressing surplus dishes into service at a fraction of the cost of a new unit. Of course a low noise converter can be purchased at quite reasonable cost ($699) and so can a receiver such as the one reviewed in this article. The conclusion of this preamble is that provided one is prepared to purchase a few hundred dollars worth of electronics, and to scan the surplus market for a suitable dish, good results are achievable at a fraction of the cost of a full earth station. The receiver The Dick Smith receiver tunes the frequency range from 950MHz to 1450MHz. The incoming tuned signal is mixed with the receiver's local oscillator to produce an intermediate frequency (IF) signal of 70MHz. This 70MHz IF is then converted to a baseband signal which consists of composite video and audio subcarrier signals. What makes this receiver special is the provision of user controls for both IF bandwidth (ie, at 70MHz) and audio bandwidth. This is a most necessary feature due to the variation in the signals that can be received. If the receiver was supplied with a fixed IF and audio bandwidth, optimum results could only be obtained with a signal that fell entirely within the fixed ability of the receiver. By making the IF bandwidth adjustable, the user can narrow the bandwidth to receive weak signals, and widen the bandwidth to receive strong signals. Apart from this, some satellite transponders ·operate with a bandwidth of 36MHz while others operate at 18MHz. Trying to squeeze 36MHz into an 18MHz "window" causes distortion and trying to receive an 18MHz transponder with a 36MHz receiver bandwidth allows so much noise into the system that the signal may well be unwatchable. The same applies to the audio bandwidth. Trying to receive a 200kHz wide audio signal through a 15kHz filter would render such a high level of distortion as to make the audio unbearable. Conversely, This photo shows the front panel layout of the receiver. The polarity controls are not used for Intelsat reception and could be rewired for the AFC defeat function. 42 SILICON CHIP The rear panel of the WR-3500 satellite receiver. The 70MHz "loop" connections allow the use of special interference filters if required. This is an "off air" shot of Cable Network News (CNN). This is another "off-air" shot, this time of the US NBC weather forecast. The construction is typical of most receivers, where one circuit board suits many models, hence the "missing" components. trying to receive a 15kHz audio signal through a 200kHz filter would provide little recovered audio. So we can see just what a valuable set of controls this receiver provides, by allowing the user to match the receiver parameters to the incoming signal. Another handy provision in this receiver is the accessible 70MHz "loop", allowing the insertion of filters in the IF strip, should there be unavoidable terrestrial interference. (It is a pity that the 4GHz satellite television band is also used in many areas of Australia for the distribution of data and terrestrial television signals). Apart from these features the receiver is pretty much a standard design, providing feed horn polarity and trim controls (never used for Intelsat reception), and adjustable audio tuning between 5.0MHz and 8.0MHz. Transponder tuning is made via the large control on the right hand side of the unit. On the rear of the unit are the two bandwidth controls, the 70MHz loop connections, composite video and audio outputs, a video inversion switch (originally used in the early 80s as a simple video scrambling method), an RF output for connection to a television set, and a tagstrip containing connections for polarity adjustment of the dish feedhorn. A video level control is accessible through the rear panel to allow for adjustment of the video output signal when using a monitor. The port labelled "SCPC" is not used. One feature that has not been provided is an "AFC disable" switch. This feature is useful when TI [terrestrial interference) is encountered, or when two adjacent transponders are being received. With the AFC enabled at all times, the receiver AFC tends to lock on to the strongest signal, which in some cases is a distinct disadvantage. continued next page APRIL 1989 43 The modulator used in the receiver is a PAL type. Connecting this to a PAL television set provides a black and white picture with sound. The modulator sound subcarrier is fixed at 5.5MHz as used in Australia and most other PAL countries. vcc .0047 .01 13 2.2 2.2 62k 11 15 Vi NE571 14 10 - F--OVout 10 16 Testing During testing against our benchmark receiver, we noticed that a considerable improvement in audio signal to noise ratio was achieved by using a simple NE571 audio expander. This unit is inbuilt in our reference receiver and the circuit appears in Fig, 1. It could easily be added to any satellite receiver for improved audio. Overall, the DSE WR-3500 receiver provides good performance and with a few modifica- 1-2.2'.i 12k ..,. 200pFI 200pFI .,. .,. ..,. Fig.1: this simple expandor circuit can be used to improve the audio signal to noise ratio from a satellite receiver. tions will easily perform as well as the best commercial units available overseas. It is very reasonably priced at $749.00. For further information on the WR-3500 satellite receiver, contact Dick Smith Electronics. They have a free Satellite Information Pack which is available from any of their stores. Roadrunner AR 900 handheld scanner The Roadrunner AR 900 is made by the well known Japanese communications company AOR (named after the call-sign of the company's founder, JA1AOR). It is the latest offering in small handheld scanners covering the cellular telephone band. The unit covers four frequency bands: from 60-90MHz, 11817 4MHz, 430-512MHz and 830950MHz, which should make it of particular interest to those interested in the higher bands. Five banks of 20 channels and a scan rate of 15 channels per second make for ease of operation, as the user can program a particular bank of channels for a dedicated service. For example, 20 aviation channels could be programmed into one bank while 20 marine channels could be resident in another, and the AR 900 will then scan these "service" bands extremely rapidly. Channel spacings Inbuilt and user selectable channel spacings of 5kHz, lOkHz, 25kHz and 30kHz ensure that all possibilities are covered, unlike other units on the market which do not allow correct reception of all frequencies. In fact, this is the only 44 SILICON CHIP scanner we have seen with the correct increments for the cellular telephone band. Some 25 front panel keys allow user control of all functions including scan delay, hold, skip, priority, up-down scanning, AM/FM selection, frequency search limits, search and scan. The LCD readout has a backlight switch which can be latched, a great improvement on the more commonly found "momentary on" controls. There is also a keyboard lock control to prevent inadvertent corruption of those carefully programmed frequencies by curious fiddlers. The AR 900 uses an EEPROM (electronically erasable programmable read only memory) as the permanent memory system which ensures that no reprogramming is necessary should the inbuilt 6V nicad battery run low. To ensure best possible reception under varying circumstances, the unit is supplied with two separate whip antennas. The thinner of the two gives best results on the UHF bands, while the thicker, helically wound antenna should be used for lower frequency operation. The instruction manual is generally quite good, apart from strange spelling in some places, probably resulting during the translation from Japanese to English. The audio output is a little on the low side although is quite adequate when the earphone is used. Whe·n the receiver is muted it does produce an audible hiss although this is really only noticeable when listening in a quiet room. However, This is a top view of the AR 900 scanner, showing the controls and antenna socket. _!:!undreds of other items not listed - Send 40c ·postage stamp for list 0. ~ ©[F{]&~[l&OO I ~ I [b□~□ 122 PITT ROAD, NTH CURL CURL ~ a ~ g. 0. ~ MAIL D.RDERS: BOX 156. DEE WHY. NSW 2099 1ELEPHONE (02) 905 1848 SUPER SPECIAL al ~ FM STEREO KITS -~ All three modules sup.plied are fully assembled and aligned. Circuit diagram supplied. ~ ONLY S22 g E p&p $2.00 g> Antenna $1 extra 5. ff 01------------------18 455kHz IF coils for valve radios ·. Osc coils . . Transistors $1 75c AD 161-162 AD 149 . Chrome push-on knobs . Slider Pot knobs . $3pair . $2 ea 10 for $1 . 10 for $1 ~ f ~1-------P-O_T_S-------~t t;; fg ¼ Meg Switch . . $1.00 2 Meg Ganged Tapped Log . $1.50 i~~~u:~c;~~~ntric .· S .50 ~ ... i ½ Meg Ganged log . . (/) 10~ ~ua~w~t~~c-entric Doubl~ $ ~~k 25k 4 Gang linear 20k Linear Single . 1 Meg Log Switch . . 1 Meg Dual Ganged l og . 100k Sub Mini . . 10kSubMini . 0.25 Meg Dual concentric . . 25k Dual Ganged Switch . 10k Dual Ganged Switch . 250k Dual Ganged Switch .. 1 Meg ¼ Meg Dua! Concentric Tap 40kDoublePoleSwitch ~-~ °g .! I ~ ~ ; z 1OOkDualConcentric . 2 Meg Linear Ganged . . . . $1.50 11. Meg Dual Concentric Linear $1.50 $1.50 100k log Switch . . . $1.00 $1.00 50k Mini . .4 for $1.00 0 1. 50 $2.00 S .50 . $1.00 . . $1.00 . . S .50 S .50 ;1:~~ ~~~kl~i;:~t~h . .. . 100k Log . . 50k log . . $ .50 . S .50 ~i;i:·_ 1_0~:1:~~ J ::-.: ~ §. $1.00 $1.50 $1.00 $1.00 I $1.50 5. -· I ~ : : ::~ 0.25 Meg linear or Log . . VU ~ .4 ;~~:~~'.near . . DUAL SPECIAL ~ ~~::~ ~ ~;kM~~a~i~~~ed Switch . . :1::~ 1.5 Meg Single . . . ... S .50 25k $ .50 ~ -g I Dynamic microphone Desk type METERS 1--s4_P_Ps_1_--1; $3 TEISCO Ceramic 1 E , · .... -.. ·--· ... . ········ .......... , pp $ Microphone R f--. ___-____-..-__.....__s_2 _PP_s_1_---1 o.§ 5 mixed rotary switches 1 2 mixed switches ~ .s! 1 a., :.' $2.50 $4.50 9 Touch micro switches 4 for $1 Mlcroswitches 5A 250V Mixed resistors: handy types 100 for $2 Mixed capacitors; handy types 100 for $2 §' TV stick rectifiers $1 each Transistor earpiece . 4 for $1 plug & lead g, S. l 1---------+---------1 0f - sac ~1---------+--------~~S, "'i al ~f----------+--------~~ The AOR AR 900 programmable handheld scanner has an amazing number of features in such a small package. It covers four frequency bands: 60-90MHz, 118-174MHz, 430-512MHz and 830-950MHz. any such quibbles pale into insignificance when you consider the overall level of performance and the amazing number of features engineered into such a small package. Recommended retail price of the unit is $599. For further information and the name of your nearest dealer, contact the Australian distributor, Access Communications Pty Ltd, 33 Alleyne St, Chatswood, NSW 2067. Phone (02) 406 5311. ~ ---------l a ... Slider Pots. . .. single sac; dual $1 .-~-- ~-------....... 250k dual 25k dual 1 Meg dual ~ 2 50k single 1k dual 2 Meg dual 50k single 1/, Meg dua.1 2 Meg single 0 ~ 10k single i~-VA-L-VE_S_ _ _ _5_A_ S4_ _ _ _ _ 12-A-X7- - - ~ ! :c I Are you about to change your address? Please advise us by the middle of the month to ensure that your next issue arrives at your new address. It helps us if you can send your old address label too. If you have any queries about your subscription call us or write to us at: SILICON CHIP, PO Box 139, Collaroy Beach, NSW 2097. $10 $10 $10 $7 $7 . 25 2 gang covers all Aust .,AM bands ; s4.75 ~ Notice to Subscribers 6V6 6K8 6B06 6B05 . EF86 EF86 6BM8 6BL8 6U7 6B05 6K8 6U7 . 6K7 "C I PP $1 for one or two ~ g GRAMO MOTOR & PICKUP §'. 1 $17.50 11-----------------ls. ) NEW PRICE ON i ... PP S3.50 NSW. ~ l-ln_te_rs_ta_te_S_4._4o_ _ _ _ _ _ _ _ _ _ _ _ I ;: ~ 15 ~f 0 VALVE SOCKETS OCTAL: 7 PIN , 9 PIN . 4 FOR $1 , ~ -6 Hundreds of other items not listed - Send 40c postage stamp for list