This is a problem in general in direct conversion schemes: and this is the
reason that "quadrature" detectors are made, with two mixing channels 90
degrees apart, so that the phasing is no longer a problem. (the sqrt of sum
of squares of the signal out of the two channels (or "magnitude") is not
sensitive to phase.)

Cliff

"Joel Kolstad" wrote in message
...
I'm curious... with the current popularity of simple (e.g., QRP usage)
direct conversion receivers, whatever happened to the problem of having to
synchronize the cariier phases? I'm looking at Experimental Methods in RF
Design, and they just use an LC oscillator for the input to the mixer.
If
input carrier is cos(f*t) and the LC oscillator is generating
cos(f*t+phi),
where phi is the phase offset between them, you end up with a cos(phi)
term
coming out of the mixer. If the frequencies are ever-so-slightly off, phi
essentially varies slowly and cos(phi) should slowly cause the signal to
fade in and out.

Why isn't this a problem in practice?

Thanks,
---Joel Kolstad