In message . com,
Radium writes
Hi:

Video signals for NTSC, PAL, and SECAM television are transmitted on
AM carriers.

My question is, let's say I have a television set that is capable of
receiving and demodulating FM video carrier waves.
I've got one (or at least the demodulator part of it). It's called a
'Grundig Satellite Receiver GSR2'. It receives German TV. I use it to
watch the German version of the Teletubbies. [Talented chaps, those
Teletubbies, speaking German without a trace of an English accent.
However, 'Eh - Oh' in German is still 'Eh - Oh'].

I also sometimes watch that English 'dinner' programme which several
German channels transmit on New Years' Eve.

Radio amateurs also often use FM to transmit TV signals. With a little
ingenuity (and maybe some modifications), you can actually use satellite
TV receivers to watch these transmissions.

What would I see on
the TV? I am aware that no company uses FM video. Would I see sawtooth-
like patterns on the screen due to frequency-modulated electric fields
present in the environment?
No. If the signal is demodulated correctly, you see normal pictures,
usually of very good quality (and in colour too, if you have a colour TV
set), created by waveforms called 'video'. Potentially, on an AM TV set,
you might be able to get some sort of poor quality picture if you could
slope-detect the FM TV signal. However, the deviation of normal
satellite signal is much too great, and I doubt if you would get
anything usable (just a lot of squiggles on the screen, like you
suggest).

I'd really like buy a TV with a FM-video receiver; I want to find out
what FM-video disturbances in the SHF [Super High Frequency ]
frequency-range look like. I am sick n' tired of AM video.
On a spectrum analyser, you see a wide FM signal, where the deviation is
caused by the 'video disturbances'. This is normal.


AM should be used for analog audio. FM should be used for digital
video.
It can be (eg where the instantaneous deviation or frequency corresponds
to the value of a digit). However, for digital signals, the boffins have
devised all sorts of clever systems of modulation. Some of these can be
thought of simplistically as a mixture of AM and FM, but some are really
complicated. These are designed to be much more efficient than 'simple'
AM or FM.

Ian.
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