"Michael Black" wrote in message
xample.org...
On Tue, 25 Feb 2014, AndyW wrote:
On 24/02/2014 08:12, gareth wrote:
Picking up on your BW comment, AIUI, the Baird transmssions of 30 line
pictures
were also of the audio BW, and were transmitted as part of the normal
broadcast,
but not at the same time as the audio; it was either speech or video,
but
not
simultaneously!
I read that.
You would think that it would be trivial to transmit on 2 channels; one
for the video and one for the sound.
But at the time, it would have been expensive, another receiver for the
second channel, two transmitters at the transmitting end. And wasn't it
the era of silent films, or at least silent films weren't that long in the
past? "Who needs the hear sound while watching a picture?"
Much later, some used ISB (independent sideband) to send SSTV and have
audio at the same time. Audio on one sideband, the SSTV signal on the
other. But that's even worse, two whole receivers and two whole
transmitters at both ends, all that selectivity and stability that
wouldn't have been available earlier.

TX could have been simpler had they combined audio and video using
quadrature modulation and a pilot tone, much as is / was used for the
colour subcarrier in PAL (also NTSC?) TV, but I doubt that anyone,
even the filthy rich (or even those who like to boast about how rich
they are :-) ), could have afforded the concomitant RX complexity
on their household budgets!

And talking of colour TV encoding, ISTR ...

NTSC - Never Twice the Same Colour

SECAM - System Essentially Contrary to the American Method

PAL - Peace At last!

BUT, didn't Logie Baird (not to be confused with Yogi Bear :-) )
do some experimentation with colour TV on the mechanical approach
anyway?