On Mon, 27 Aug 2018, Gareth's Downstairs Computer wrote:

Acquired a Racal 1772 RX which has ISB filters, but is there
any real use in amateur radio for independent sidebands?

The narrow IF filters are only available on USB, and I wonder if
they were intended for RTTY or Piccolo, for one is 800 Hz to 1.2kHz?


An obvious use would be sending pictures over SSTV while you talked at the
same time. Gives the receiving party something to do while the picture is
transmitted.

And that's the only use I've seen mentioned for ISB in ham circles. ANd
the problem is, most can't afford duplicate equipment, so it becomes a
neat thing that doesn't happen much.

You could do the same thing with RTTY on one channel and voice on the
other. I gather that did happen in military or commercial circuits.

I don't know, but an interesting thing is that if you have a continuous
signal on one channel, you get a means of "locking" to the incoming
signal, though I haven't given it much thought. There's nothing to lock
to on SSB, but an RTTY or SSTV signal in one channel always presents a
"carrier", albeit one that shifts around in frequency (but to a known
amount).

You get redundancy if you have an DSB transmitter but synchronous detector
that lets you select which sideband (or both sidebands to stereo
headphones). That's supposed to be interesting. But I can't see getting
any good effect from sending two sidebands with the same audio to both.

And if you were sending bulletins, I supposed sending English on upper
sideband and French on lower sideband (the Radio Amateurs of Canada could
do that, but I'm not sure they transmit bulletins) would simplify things,
the end user just selecting which sidebande according to which language
they wanted to hear.

It does work commercially, send two different programs at the same time,
it takes up less space than two DSB transmitters, and probably simplifies
other things.

Michael