"Radium" wrote in message
oups.com...

In TV, most systems employ a version of AM to carry the luminance
(Y) signal; the color (chroma) information is carried via a somwhat
different version of AM, and the audio is most commonly FM.
The French SECAM system as originally implemented carried the
chroma information on TWO frequency-modulated subcarriers.

Why not carry the luminance-signal on FM and the audio-signal on AM?

The reasons (primarily) behind using the AM visual and FM aural signals for
television a

Visual: Bandwidth. Visual uses what is called 'vestigial sideband'. This
means that basically only one sideband carries the modulation, with only a
vestige of the other sideband remaining, thereby reducing the bandwidth
needed for the visual signal by a significant factor. If FM were used, the
entire symmetrical waveform would have to be used, and would use a lot more
bandwidth. (Analog satellite television does/did use FM modulation, on the
order of 36 MHz IIRC, but bandwidth in the GHz ranges isn't at as much of a
premium as on relatively crowded VHF and UHF frequencies

Aural: Coverage. The aural signal (which is sent separately from the visual)
is only about 10% of the power of the visual signal.