[HBR] Dual conversion schemes

[Ian Wilson]

Not HBR but I hope to gain some insight here.

I have prototyped a receiver using a 1.5-3Mc Collins PTO as the LO in a
dual conversion
setup. The scheme for 40m (as an example) is:
  - 10.247MHz crystal oscillator
  - 3.072MHz 1st IF (I had some nice canned filters available)
  - PTO around 2.617 Mc
  - 455kHz second IF (xtal filters available for this frequency)

This has some rather large birdies; for example, LO on 2.676MHz has 4th
harmonic
that is 455kHz away from the 10.247MHz xtal oscillator.

On the general principle that most of the frequencies in the original
scheme are
too low, here is a different scheme intended for some Racal 10.7MHz xtal
filters that
I have:
  - 20MHz crystal oscillator
  - 12.9MHz 1st IF (will use a double-tuned bandpass filter)
  - PTO around 2.2 Mc
  - 10.7MHz second IF

10.7MHz is more difficult to tame than 455kHz but still feasible even with
6BA6's.
I may split the IF and mix down to something for an AVC amplifier stage.

Does anyone spot any obvious problems with the new scheme? How about on
other ham bands? Thanks for looking.

73, ian K3IMW