The system in use was the same as for commercial TV,in accordance with the rules of C.C.I.R.: so the receiver was a common television with a simple frequency converter. The transmitter had to be homemade because at that time there was anything ready in commerce:video cameras were the ones used for video entry phones.
A received image picture, printed generally by a Polaroid photo camera, is enclosed to the QSL card.
A very popular ATV transmitter was described by DJ4LB on VHF COMMUNICATIONS. Some other works by G6ADL (hybrid circuit), by G6AFF and by some Italian OM have been interesting too.
The signal needs amplifiers strictly in class A, so powers were low (about 1,5 W) and more important was the antenna’s gain.
After some months of tests IW2BFP and I2YOT published an article about A.T.V. system, stimulating the A.T.V. national manager I2ORX. We thank him till now for his help.
Actually our activity in A.T.V. is practically null because we don’t know anybody operating on this mode at 1.2 GHz.
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Picture in the top-left corner. Video GBC Mark XIV with a 1/2" Plumbicon tube.
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We will never forget this contact.
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When the private televisions were not so common, IW2BFP and I2YOT were transmitting this picture |
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I began seriously my activity in A.T.V. when I read an article by I2ORX, Giampaolo and I2NFB, Franco: it was published on Radio Rivista n°1 in 1979 and described the construction of an ATV transmitter using DJ4LB’s circuits, that appeared on VHF Communications. I had dedicated my tyme before to antennas and receiver converters; then , with elementary circuits, I began to transmit grids and chessboards painted by Commodore 64 and then I realized also the Tx DJ4LB with a videocamera. I began to change some circuits in this project with some new ones, till the ATV transmitter was completely home made (IW2BFP TX). So I realized a very compact video transmitter that was using directly the frequency 434.250, instead of a subcarrier of 38,9 MHz. The construction proved to be sure and valid, but unfortunately, after some months, ATV transmissions in 70 cm. were forbidden in Italy. In some other countries, with any prohibition, the transmitter has been well accepted and most successful. The activity in 1.2 Ghz has been very poor both for realizations and for distances (only in the city of Milan). When I moved in Pizzoli, I stopped completely every ATV activity.
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On the left a block diagram of the ATV transmitter BFP 70. On the right. The modulator, BFP 3, the one survived after the demolition.
Electrical diagram of the ATV modulator BFP 3 ( negative amplitude modulation ) at 434.250 Mhz.
Some other parts survived to demolition. On the left. Interstadial coupling with helicoidal filters between mixer and driver in ATV TX by DJ4LB. In the center and on the right. Two cavity oscillators for some AM A.T.V. |
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I calculate after some tests that a 0.75 mm reduction will be good. In the upper left picture you can see a Siemens original ceramic resonator and the oscillator circuit that I used in order to test the frequency. The frequency meter was an HP 5245 L with a plug-in unit 5254B. I prefere this counter because the tuneable cavity and the voltmeter permit to measure the harmonics too and relatives amplitudes. After a 0,72 mm reduction, I obtained the frequency of 1240 Mhz. On the right you can see a 1,2 Ghz output stage with some 85 watt power on FM phone. We believe to be active once again on ATV next spring. If our transmitter will be reliable, we will describe it on this page.
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