[Milsurplus] Crystal filter question(s).

[C Whitaker]

de WB2CPN
My experience is with the BC-779* while
in USAF. 1946 until the SP-600's came out.
First, the resistors control the width,
i.e. Half-Power points.  The Phasing control
moves the notch within the bandpass so that
an interfering tone can be nulled out.  It
shouldn't affect the shape of the bandpass.
The depth of the null depends somewhat on the
resistors and bandwidth, but not much.  The
frequency at the bandpass peak should not
change, but very important, use that frequency
to align the IF's and the BFO.  It could be
a slight bit different from the "Book" IF
frequency.  BFO's need to be variable because,
(1) it can zero beat a second interfering CW
signal, and (2) different radio operators work
their best with their favorite tone frequency.
Note:  The crystals they used were rejects
during some other manufacturing process, low
activity or whatever, but will work in passive
circuits like IF filters in BC-779's and
similar receivers.
73  Clete