raypsi wrote:
Hey OM

This thread begs the questions:
What about SSB and CW? Would syncro conversion detect just the upper
sideband?

It is not possible to use synchronous detection with SSB or CW because
there is no carrier in the signal. So the circuit that recovers the
carrier will work on the modulation and the result is unusable.
(i.e. no audible modulation with SSB, and at best a 0Hz tone with CW)

Because the lower sideband would be below ZERO hertz?
If you use a BFO how do you get below ZERO hertz?
Doesn't the Fourier transformation of the mixers' LO and rf input in
a syncro conversion produce frequencies below ZERO?

There are no frequencies below zero. When you are using only a single
mixer, both sidebands will produce frequencies above zero. And there
will be no suppression of the "unwanted" sideband.
(the synchronous AM detector is a dual-sideband detector)