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My interest in this mode is concentrated on the 23cm and 3cm bands.Equipment in use is mainly home-brew either from kits or published designs from various specialist publications. 23cm equipment consists of Quadloop aerial,home-brew 2watt PLL transmitter with intercarrier sound(audio & video both filtered) driving a 18watt brick PA,various ex satellite receivers used in conjunction with home-brew gasfet preamps and purpose built receivers. 3cm equipment consists of ex burglar alarm gundiode doppler modules,home-brew video and audio drive circuits for transmit,converted LNB’s are used in conjunction with 23cm receivers both are fed with 20db horns or small dishes.Due to location activity on this band is from portable locations,usually on high ground on the Lincolnshire Wolds. Video drive sources are from various camera’s or home-brew Test Card Generators. Recent projects include 4 way PIC controlled Video Switch,PIC based Test Card Generator from the PICDREAM design, software modified to give callsign instead of clock,this design can be recommended to anyone wanting a simple low component count TCG (see CQTV from BATC for details), playing about with old LNB’s to convert into DRO stabilized FET amp Transmitter. |
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Getting Started No apology here for suggesting the use of satellite receivers,they’re cheap,ready built and aligned and are capable of good results if a few basic modification’s are undertaken.As our commercial friends for who these receivers were designed for use greater video deviation than we do the first requirement is to increase the video gain,this can often be as simple as turning up the appropriate control(usually marked VIDEO GAIN),if not enough adjustment is available a few component changes in this area usually does the trick.In the UK we use 6mhz intercarrier sound so the receiver should be set accordingly,usually variable on older receivers,may be software controlled on later.Some may require a little work in this area. As most aerials present a short circuit as far as DC is concerned the LNB supply that is present on the RF input should be disabled or made switchable. Various aerials are available from the Quadloop,Yagi and Bowtie designs,for single aerial work it must have a bandwidth of aprox 70mhz to be used at the simplex and repeater i/p frequencies and the o/p frequencies(1248,1249mhz repeater i/p 1310,1316 repeater o/p,1260mhz approx. for simplex. If your lucky and live near a ATV repeater or an area of activity you should find some pictures quite easily(a preamp will be needed for long distant operation) a call on the talkback frequency of 144.750mhz may bring help or assistance. |
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Me and Alan G0KOO 3 cm portable on the Lincolnshire Wolds nr Caistor P4 pictures on Horn P5+ on Dish from GB3XY |
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12-13 August 2000 Microwave ATV Tests |
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After a chance phone call to Bob G8OZP and having access to the family static caravan on the east coast a small amount of 3cm ATV gear was packed along with the family.On arrival a P5 picture of Bob was seen with the LNB poked out of the window He had also chosen Southwold and was only 200M down the road.Leaving the rest of the family to unpack I set off to see what was going on,P5 pictures of PE1ECO were being received by Bob,a few hours of chat and viewing followed,Bob then decided to head for Bridlington for the next day. I set up on the Sunday and after a phone call to Bob to get Hans on the west coast of Holland to point my way a P5 picture was soon visible.This was my first experience in sea ducting propagation and after an hour Hans reported my signal was also P5 not bad for 10mw and a 20db horn. Stations in contact with were PE1ECO/P,PE1DCD/P,PE1PSJ/P all P5
Also seen was a quad type screen with inputs on 23,13 & 3cm with PE1RJU on,was told more than likely to be PI6TNO repeater |
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August 2001 Microwave ATV Again located at Southwold,unfortunately had to be cancelled due to very poor weather conditions in the UK and Holland |
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