Hi Len,

Avery Fineman wrote:
For narrowband voice, SSB AM is just dandy and a phasing system
using the Gingell-Yoshida polyphase network is quite easy and
error-tolerant to make a good phasing exciter. It can be used in
"reverse" to get an easy-to-select sideband demod or an ordinary
AM detector that yields false stereo (one sideband to each ear),
already done with simple CW receivers.

....or real stereo! The Kahn/Hazeltine AM stereo sysem did this -- L in the
lower sideband, R in the upper. Hence envelope detectors recovered L+R, and
AM radios built back to the beginning of (radio) time kept working.

On the other hand (and I know this is just asking for abuse), the Motorola
C-QUAM AM stereo system could be applied to SSB modulation and still work,
which obviously Kahn/Hazeltine can't. I don't imagine C-QUAM's designers
were considering this, however.

It's almost painful to look at the (complex) envelope of AM and notice that
the quadrature signal is completely unused. Sending stereo over I and Q
strikes me as a 'interesting,' (does anyone know of a commercial system that
does this? Surely somebody's must...) but of course it would break
compatibility with current receivers and I imagine someone who's more
knowledgeable than I could point out some pitfalls as well.

---Joel