[Milsurplus] Crystal filter question(s).

[Bill Cromwell]

Hi Ron,

I did a workup on the passband of my Hammarlund HQ145-X a number of
years ago (I don't have it now). I did not note any change of center
frequency when changing the bandwidth... the changed resistors you
referenced. If there was a difference it was smaller than my amateur
means of plotting the passband. The shape of the passband obviously
changed but I didn't observe a change in the main peak. The phasing
control did shift that a small amount. Of course...there is a BFO
frequency control there, too. In practice I didn't have to change the
BFO when I made changes to the phasing control. I always thought a
crystal controlled BFO would have been acceptable.

By the way... That single-crystal filter for all its "simplicity" was
very effective. I used that receiver in traffic nets and even in some
casual contests (in the 1980s) and it did a very good job for me. If
somebody wants to reduce parts count, receiver size, and expense this
should be considered. The ARRL Handbook dismisses it as being too simple
for practical use. I have a project on my bench to do just that.

73,

Bill  KU8H