Hi Dave,

Thanks for the information; it's quite helpful!

I was (am) committing the faux pas of feeding the mixer output directly into a
narrow bandpass filter...

For example, the popular
Mini-Circuits SBL-1 mixer seems to have LO-to-IF isolations of
anywhere from better than 65 dB (at HF) down to around 30 dB (at UHF).
If you're trying to tune a weak signal (say, 80 or 90 dB weaker than
the LO signal) then the residual LO feedthrough can cause the sort of
swamping you're seeing.

So... say I'm using a 45MHz IF, trying to tune 414MHz using the SBL-1 and an
LO of 414-45=369MHz (low-side injection) at the SBL-1's recommended +7dBm.
Presumably I'll see a 7dBm - 30dB (LO-IF isolation) = -23dBm signal at the IF,
but it should still be at 369MHz, right? How does the LO "bleed through" to
the 45MHz IF... and what power level should I expect to see there?

---Joel