I have just finished my initial design for my BFO and am trying to decide on its correct frequency. So far I have the following details of the crystal filter it will be working in conjunction with:
crystal filter center: 9.998887MHz
insertion loss: 1.8dB - 2.6dB
-6dB points: 9.997667MHz and 10.000107MHz (2.44kHz wide)
-60dB points: 9.991216MHz and 10.002573MHz
BFO frequency: 9.998000MHz
From what I have read I think the current BFO frequency is a little low and it should be around (9.998887MHz + 2.5kHz) so 10.001387MHz.
Would it also work if I set the frequency to (9.998887 - 2.5kHz) so 9.996387MHz, I think it may be easier to lower the BFO frequency rather than raise it.
My receiver is going to be working on the 40m band, so I need to be getting the lower side band when listening, assuming I am just tuning via a capacitor or potentiometer driven VFO (have not decided yet) would it matter which of the two frequencies I chose as the BFO frequency as when tuning the lower side band signal would pass through the crystal filter's pass band at some point and so beat against this frequency?