I've been playing around with some homebrew superhet radios, and I'm finding
that a significant amount of energy ends up at my 1st IF frequency that seems
to be coming from the LO. While I expect to see energy from LO+/-IF end up at
IF, of course, I've checked the LO+/-IF spurs (the LO is coming from a
PLL-based synthesizer), and in general it seems that a lot more energy ends up
at the IF than what the spurs alone would suggest. I remember a talk I
attended where the presenter mention that one of the biggest problems with
building receivers was "the LO getting into the IF," so I'm thinking this is
what he meant? Are there other less obvious paths for the LO getting into the
IF than just the LO+/-IF spurs?

The signal right at the IF eventually gets turned into DC and hence filtered
out, so in theory it doesn't really matter that much, but in practice with
very weak signals eventually the IF feedthru is stronger than the weak
signals, so it limits how much amplification I can provide and hence limits
the ultimate sensitivity of the receiver.

Thanks,
---Joel Koltner