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.

Michael


The bloke who invented thermal socks should have thought of that.

Andy