HEATH Digest - 30 Jun 2002 to 1 Jul 2002 (#2002-181)

[Glen Zook]

One possible solution, if the crystal has migrated to
the high side of the desired frequency, is to put a
small variable capacitor across the crystal (about 25
pf maximum).  Sometimes you can "pull" ("warp") the
crystal to the correct frequency (at least near enough
to avoid problems with the filter passband).  You can
replace this with a fixed capacitor of approximately
the same value as where the variable comes out if you
like.

I had one of the crystals go high in my Collins 32S3
(these are in the 455 KHz range, much lower than the
SB-102 and thus harder to pull very far).  Put a
capacitor across it so that the frequency was back on
track for transceive operation with my 75S3A (went the
fixed capacitor route after finding out how much to
add).  Had it that way for several years before I
finally got a new crystal.

You can try adding inductance in series if the crystal
has gone low.  However, this is not as easy as when
the crystal has gone high.  Of course, the best thing
is to replace the crystal.  But, it is definitely
worth a try if you have a small trimmer capacitor and
if the frequency has gone high.

Glen, K9STH



--- Eddy Swynar <gswynar at DURHAM.NET> wrote:

If it's off by more than even a couple of hundred
hertz from the center of the IF filter passband, it's
time for a new crystal!

=====
Glen, K9STH

Web sites

http://home.attbi.com/~k9sth
http://home.attbi.com/~zcomco

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