i thought TV used 600 - 700 plus MHz, channels
ATV = Amateur TV as in TV done by amateur radio operators
This is real TV as in 25 frams / sec. Not to be confused with SSTV (Slow Scan TV)
which isnt TV its just sending individual pics as a data transmission from your computer.
There are 2 forms of analog ATV...
1) the standard VSB Visidual SideBand. This is the commercial standard for TV transmission mode for analog TV. The video is used to AM modulate a carrier, then one of the sidebands is partially removed, usually by filtering.
The audio is applied as a subcarrier FM signal and is usually offset from the main carrier, commonly 5.5 or 6.5 MHz. Depending on where you are in the world.
2) the other form that is mainly used by amateurs, mainly cuz its a heck of a lot easier to set up, is straight FM TV. This time both the video and audio use FM. Again the Audio subcarrier is offset from the Video by 5.5 or 6.5 MHz
For either system the total bandwidth is ~ 7.5MHz per channel
A lot of amateurs have, in recent years, also been playing with digital TV and in general use the same modulation modes used in terresterial DVB systems. This means we can use DVB TV settop boxes (which are readily available and cheap) to demodulate our signals.
Some guys do use the mode s that satellite TV uses and they make use of the satellite STB's for decoding.
I have built up ATV gear on 1.2GHz, 2.4GHz, 5.7GHz 10GHz and 24GHz using FMATV
on 24GHz we are using a 80mW Gunn Oscillator transmitter into a 40dBi gain dish and getting an easy 76km.