Mark Zenier wrote:
In article . com,
wrote:
I just don't buy the argument that nobody thought about DSB. DSB is
naturally generated from a mixer if the audio signal is zero mean.
[Again, it is best to talk about modulation schemes by discussion
modulators.] Remember, AM exists because the demod is cheaper, not
because it is any easier to generate that say DSB. AM and DSB use the
same hardware.

But there's something where a DSB local carrier has to be in phase with
the signal, otherwise there some sort of canceling effect from the two
sidebands. SSB doesn't have the problem, it just causes a pitch shift.

I've done DSB generation in a baseband signal for a telemetry
application, similar to the FM stereo demod, i.e a pilot was provided.
However, say you had no pilot and you were simply tuning by hand.
Assume a simple mixer. If you were off a bit, the sound would be pretty
ugly, i.e. 1000hz would be a combination of 999hz and 1001Hz if you
were off by 1Hz in the local carrier. However, I could see this making
tuning very easy since if you were off a little, it would be clear that
the local carrier needed adjusting.


The only DSB I know of, (that isn't just treated as a cheap form of SSB,
where really only one sideband is used) is the L-R subcarrier in FM stereo
where they double the pilot tone to get an in phase carrier.

Mark Zenier
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