"John Ferrell" wrote
Crazy George wrote:
The audio is not mixed with the main carrier?
It can be either way.

TV aural uses a separate transmitter from TV visual, because the visual
amplifier in a TV tx is not linear enough to amplify both the aural and
visual waveforms while maintaining r-f intermods sufficiently low (to FCC
spec). The aural and visual signals are combined with mutual isolation of
the txs, and radiated by a single antenna, typically.

In an emergency, TV stations sometimes combine A&V at exciter level and pipe
them through the visual PA, which is operated at reduced power to minimize
r-f intermods. Typically the TV station is not meeting spec then, however.

If you choose to use separate transmitters the demands
on antenna bandwidth are greatly reduced.

Reducing antenna bandwidth needed also would require separate antenna
systems for the aural and visual transmitters. That is done, occasionally -
but not often. This doesn't reduce the bandwidth needed by the visual tx by
very much, however. Generally it's more cost-effective to use a single
antenna to radiate both A&V.

RF (RCA Broadcast systems field engineer, 1965-1980)