Fred McKenzie wrote:
Addressing the original question about direct conversion, what if you
used a temperature compensated oscillator with a phase-locked-loop? If
the assumption could be made that the broadcast station will not drift,
then you could tune each station dead on with an RIT-like adjustment of
the oscillator.

I'm thinking the better, potentially workable solution is to just use a
feedback loop (I'd say a Costas loop, but I'm not convinced this is the best
option for AM -- just looking at the DC component of the Q output of the
mixer gets you sin(phi), where phi is the phase difference between your LO
and the incoming RF, which seems better as an error term than the Costas
loop's error term, which is something like I*Q (before low-pass filtering)
and gets you something like m(t)^2*sin(2*phi) and therefore has the
potential to add different DC offsets due to the m(t)^2 term).

What I'm really planning to do is to build a quadrature receiver first and
then see if I can build the feedback loop in software. If not, at least
I'll be able to receive SSB and regular AM -- just not AM IQ binarual
stereo, AM C-QUAM stereo, etc.

---Joel Kolstad