Mike WIA and I performed some testing today. I have uploaded some graphics of
the crystal filter characteristics. .002Mhz per horiz division , by -6db per
vertical division. Base of skirt at -54db.

Not a bad shape really just about 2.7Khz, which is OK. Ripple is a bit violent
but should still be OK.

Filter skirt was at -40db, which is OK

Centre frequency was a bit low so to pass USB the LO will need to be set to
9.996Mhz. (In Mikes example). The marker spot is set to that frequency.

The insertion loss was -17db, which is higher than expected. Not sure why. Some
of that could be a mismatch to the test rig, but I was using the pre-amplifier
stages. I was estimating the mismatch may give rise to about -6db insertion
loss. More work needed on that to find out why.

Mikes audio pre-amp was not working as expected and time ran out, Mike will test
that stage again.

NOTE. If we use a dynamic or crystal microphone a series 1uF capacitor is
needed.

Happy solder smoke.

Michael