ATV on 10 GHz
The television set
The standard in amateur television on 10 GHz is the standard used in satellite broadcasting, except for large DX where the excursion is reduced.
Thus the receiver will be a commercial receiver, preferably Bi-standard PAL-SECAM (in Europe) but amateurs use more and more PAL standard.
It is necessary to avoid the too sophisticated TV sets which pass on a blue screen when the signal weakens, they make very difficult the search of weak signals.
The satellite receiver (tuner)
Any satellite receiver covers at least from 950 MHz to 1750 and now 2050 MHz; the idea is to put a modified satellite head in front of this satellite tuner.
The first tests consisted in lengthening the input lines of a TELECOM satellite head to make it functioning in supradyne mode.
Simpler now, with the dual bands heads allowing it, one removes the resonant ceramic of the upper band, and by approaching it to the other ceramic of the lower band oscillator, le lower band oscillator slips to the amateur band.
The standard is frequency modulation, with one or even several sub carriers; at least one for the sound, the whole area from Marseille to Narbonne was standardized with sub carrier sound at 6,5 MHz; 16 dB below the picture carrier.
The levels are the same ones as on1255: when one puts 1Vcc video to the input of the transmitter, the correspondent must obtain exactly 1Vcc video at the output of his tuner.
For the sound, when one puts .5 Vcc audio to the input of the transmitter, the correspondent must obtain exactly .5Vcc audio at the output of his tuner.
There were descriptions of transmitters these last years, in general, the 10 GHz is produced by a DRO.
The DRO oscillator is frequency modulated by the vidéo+sound sub carrier; sound carrier itself modulated in FM.
One gets already between 20et 40mW at this level, which allows the connection between F5ZAJ (Marseille) and F5ZFI (Nimes) at a distance of 110 km
One can amplify up to 150 mW as on F1ZGM or F5ZGN (Aigoual). The Watt is reasonably reachable (F5ZMP Lure Mountain).
With DRO oscillators, video qualitie is not so good as with varicap VCOs. Our project now, is to use a VCO on 2500 MHz and to get 10 GHz by multiplication, in order to obtain the same quality as on 2320MHz.
In television, the least decibel counts, one can receive television locally with a small horn, it is what we use at the Aigoual mount with F5ZGN (17 dB horn ), but it is 1650 m high.
The maximum must be done at the antenna , it is necessary to use a parabola, generally fed by a small horn. 40 cm are a minimum; 60 or 80 cm are still quite easy to handle and become very effective; beyond that, directivity can become a difficulty.
Modification of a broadcast offset parabola (*)
Don't be too full of hope however, in television it is necessary to live on a hill, the contact will be possible only if there is no obstacle between the correspondents (except reflexion), and on these frequencies, a foliage of tree is an obstacle.
(*) in French
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