In message , David Looser
writes
BTW AM sound was always used with +ve vision modulation. I'm not sure that
there was a killer reason why FM could not have been used with +ve vision
modulation, but intercarrier reception (the cheap'n'easy way to receive FM
sound with TV) wouldn't work with +ve vision modulation unless there was
significant carrier amplitude remaining at the sync tips. Normally with +ve
vision modulation the carrier amplitude at sync tips was nominally zero.
Many years ago I used to be in to TV and the thought at the time(often
expressed in "Television" magazine) was that the French were
deliberately different to keep manufacturing in France, hence the
positive luminance signal and AM sound. Another example of this was
what used to be called "Peritel" which was mandated for any TV sold in
France to keep out foreigners out. Who would have known at the time
that it would spread and be adopted as the now SCART socket
--
Clive