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1, II AMATEUR RADIO By GARRY CHATT, VK2YBX Amateur television: getting started This month, we take a brief look at amateur television and the equipment needed to get started. As well, there's a handy list of amateur TV repeaters and ATV groups. One of the most technically challenging aspects of amateur radio is the transmission and reception of television signals, on the amateur bands. Old timers and newcomers alike find this medium most satisfying, as most of the equipment used is "home brewed" , and program material is mostly of a technical nature. There are many types of amateur television, ranging from "slow scan" TV (SSTV) which utilises a channel width of only 3kHz, and sequential scanning at an audio rate, to "fast scan" TV (FSTV) which utilises a channel width of 7MHz and transmits 25 pictures per second. As SSTV allows a greater concentration of energy in a smaller portion of the spectrum, the distances over which communica- tions can be achieved are much greater than when using FSTV. Nevertheless, distances exceeding 400km have been achieved using fast scan TV. Reception It comes as no surprise to discover that the majority of ATV (amateur TV) activity occurs on the UHF bands, primarily due to the overlap between commercial UHF television and the 570MHz ATV band. This greatly simplifies the equipment required for reception. In fact many operators use a standard band 4 UHF TV antenna and a UHF television receiver for ATV reception. Naturally a dedicated antenna for UHF channel 35, low loss feedline, and a GasFet preamp will Fig.2: test patterns similar to this one from VK2YBX are often used during ATV test transmissions. provide superior performance, but it can be seen that very little outlay is required to receive ATV. Just as an enormous number of repeaters serve the VHF and UHF FM nets, so too do a number of ATV repeaters. In fact most activity in capital cities is via the local ATV repeater (see Table 1). As can be seen from the repeater listing, the majority have their output on UHF channel 35 (575-582MHz), so that once a suitable antenna has been obtained, it is simply a matter of determining the location of the nearest repeater, tuning your UHF television to channel 35, and waiting for a signal to appear. Many ATV repeaters are sponsored and maintained by the relevant state branch of the Wireless Institute of Australia (WIA). The WIA transmits a weekly 30-minute news broadcast, normally on Sunday mornings. These broadcasts are ideal for tuning receivers and adjusting antennae. Transmission Fig.1: some amateurs prefer to build rather than buy equipment. This photo shows a typical home-made amateur TV station. 76 SILICON CHIP As with commercial television broadcasts, the vision transmission Table 1: ATV Repeaters in Australia Location Callsign Vision 1/P Sound 1/P Vision O/P SoundO/P Canberra Wagga Wagga Sydney Springwood Newcastle Central Coast Bendigo Melbourne Brisbane Brisbane Central North Central North Adelaide Adelaide · Hockham Perth Perth Devon port North West VK1RTV V.K2RTW VK2RTV VK2RTS VK2RTN VK2RTG VK3RMZ VK3RTV VK4RAT VK4RTV VK5RCN VK5RCN VK5RTV VK5RTV VK5RWH VK6ROD VK6RUF VK7RAE VK7RTV 426.25 444.25 426.25 444.25 426.25 426 .25 426 .25 444 .25 444.25 426.25 426.25 579 .25 426.25 444.25 444 .25 426.25 426.25 444 .25 444.25 431.75 449.75 431.75 449 .75 431.75 431.75 431.75 449. 75 449. 75 431 .75 431.75 584. 75 431.75 449.75 449.75 431.75 431 .75 449.75 449.75 579.25 579 .25 579.25 579 .25 579.25 579 .25 579 .25 579.25 579 .25 579.25 579 .25 444.25 579.25 579.25 1246.25 579.25 579 .25 579.25 426.25 584.75 584.75 584.75 584.75 584.75 584 .75 584.75 584.75 584 .75 584.75 584.75 449 .75 584.75 584.75 1251 .75 584.75 584.75 584.75 431.75 sidebands and a sound carrier, the channel spacing approaches 12MHz. This sort of channel width would severely limit the number of available television channels, so a system for reducing the required channel width was developed for commercial TV stations, which is also used by ATV operators. The Vestigial Sideband (VSB) system, also sometimes known as Asymmetric Sideband (ASB) system, involves filtering out the majority of the upper sideband of the vision signal, reducing the channel width to around 5MHz. By careful compensation in the receiver, the video distortion that would normally result from the removal of most of one sideband can be reduced to negligible proportions. Sound transmission is FM, and although the techniques are similar to those used for NBFM, the deviation is much greater (50kHz). Because of the exclusive nature of ATV and the resultant lower level of activity, there are few commercial suppliers of suitable ATV equipment. The South Australian ATV Group, part of the SA branch of the WIA, has a number of Fig.4: superior results can be obtained by using a resonant antenna. This 580MHz Yagi gives BdB of gain and is available from Dick Smith Electronics. Fig.3: a portable colour or b/w camera is suitable for amateur TV. The composite video output from the camera is fed directly to the transmitter. is amplitude modulated (AM), whilst the sound is FM. Normally the sound transmitter runs about one tenth the output power of the vision transmitter, where two separate transmitters are used. However, some operators mix the FM sound at the vision transmitter output stage and consequently run even less audio power to minimise intermodulation products. The standard spacing of 5.5MHz between vision and sound carriers is used to maintain compatibility with domestic receivers. The channel bandwidth is 7MHz. Wide channel spacing is required if good linearity and adequate video bandwidth is to be obtained. With a standard AM transmission of 625 lines (25 frames per second) with two Fig.5: this is the test pattern from VK2RTS at Springwood in NSW. JA NUA RY 1988 77 Fig.6: 1W amateur TV transceiver from PC Electronics, USA. Table 2: Active ATV Groups • Gladesville Amateur Radio Club TV Group (PO Box 48, Gladesville, 2111 , NSW) . This club conducts test transmissions on UHF channel 35 on Wednesday evenings 7 .30pm-10.30pm, Friday evenings 7.00pm-1 0.00pm, and Saturday and Sunday evenings at various times. The viewing audience extends from 1 00km south of Sydney to the northern suburbs. The VK2RTV transmitter runs 20W output into a 9dB omnidirectional antenna. Contact Keith VK2ZZO for further information. • Sydney ATV Group (SATV Group, PO Box 84, Hazlewood, 2779, NSW) . This group operates repeater VK2RTS (output UHF CH35) . Operation by touch tone. Liason net operates on 14 7 .3M Hz simplex every Tuesday evening. VK2RTS re-transmits material from the VK2RTV test transmissions on Saturday at 7 .30pm. • South East Queensland ATV Group (SEATV Group, PO Box 3 , Chermside, 4032, Qld) . VK4RTV repeater input is via valid television signal. 70cm liason frequency is 438.025MHz. 2-metre liason frequency is 14 7 .3M Hz. Repeater receive antenna can be rotated by touch tone operation. • Wireless Institute of Australia. Most divisions have an active ATV group. Many state divisions stock ATV publications. See your local phone book under WIA. • South Australian ATV Gro,up (GPO Box 1234, Adelaide, SA 5001 ). The VK5RTV repeater has been licensed for 1 2 years. The present repeater is a 20W microprocessor-controlled unit located at O'Halloran Hill , south of Adelaide . Access is via a valid TV signal. The repeater has over 250 touch tone control commands, and is one of the most versatile in Australia. Regular transmissions are made on Wednesday evenings 8pm to 10.30pm, and Sunday mornings from 9am to 10.30am. A "sister" repeater to VK5RTV, VK5RCN, is located at Clare, and is powered solely by batteries, charged by a wind generator. This repeater can be cross linked with VK5RTV to provide enhanced ATV coverage form Adelaide to Whyalla and other outlying areas. • Victorian Division WIA - ATV Group (3/ 105 Hawthorn Rd , Caulfield North, Vic. 3161 ). VK3RTV operates from Mt. Dandenong and runs 1 OW into a directional antenna aimed at Geelong and Melbourne. Repeater input is via a video modulated carrier. Touch tone operation is required to activate a colour bar test pattern, and several pages of repeater information. The repeater is solid state and microprocessor controlled, and has a unique " received signal report" function. 78 SILICON CHIP transmitter, preamplifier, and receiver kits available, and it is known that the Victorian division of the WIA also had kits available some time ago. One supplier in the USA, PC Electronics (2522 Paxson Lane, Arcadia, California 91006) regularly advertises a 70cm ATV transceiver, Model TC70-1, which has met with good success in Australia. This company also has a downconverter suitable for the 420-450MHz ATV simplex (and repeater input) band which contains an inbuilt GasFet pr eamp, Model TVC-4G. One of the higher bands w hich is presently being used for FM A TV experimentation, both here and in Europe , is the 2 3cm band (1240-1300MHz). There are a number of suitable " building blocks'' which make ATV reception r elatively simple in this band. These include satellite TV downconverters which convert the 950-1250MHz and 950-1750MHz bands to 70MHz. Wyman Research (PO Box 95 , Waldron, Indiana 46182) in the USA caters for this type of A TV equipment. Recommended reading: (1). UHF/VHF Manual; G.R. Jessop (available from most amateur radio stockists). (2). The 1987 ARRL Handbook; published by the ARRL. (3.) Radio and Television Broadcast Stations 1986; Australian Government Publishing Service. .~