With all this discussion of phasing fun... could someone answer the
following question for me?

Say I'm transmitting binaural audio, with I being L and Q being R. I
receive this signal and generate my own I' and Q' outputs. However, if the
RF carrier and my LO have a phase difference, the entire IQ (phasor) diagram
is rotated by that difference and, e.g., a 90 degree difference will result
in the left and right channels I receive being swapped.

How do IQ-binaural receivers recover a phase lock to present this?

If you do the quadrature detector thing with DSB-suppressed carrier,
then when one of the two is just the wrong phase (and you get no
output from that one), the other will be just the right phase, and
vice-versa. When it's in between, does it work out right to just sum
the two? I suppose so, though it's worth going through the math to
make sure.

I went through the math and you end up with the magnitude of the original
signal. What's unclear to me is how to recover the phase offset between
your signal and the original -- although adding a DC component (or some
other unique frequency component) to either I or Q (or placed at some
strategic angle between them) would allow you to synchronize the phases.

Have any suggestions for a nice simple mixer (ala the NE602) that retains
both the I and Q signals at the output?

---Joel Kolstad