Re: Matching Xtals for Filters


From: Dana H. Myers (myers@bigboy.West.Sun.COM)
Date: Wed May 28 1997 - 15:49:56 EDT

Ed Tanton wrote:

> In a word Tim: no. It IS a thought: if you had "perfect pitch" AND a
> receiver that was stable to several cycles short term-or rather for the
> time necessary to compare enough crystals to find your matches... then
> maybe. But I question whether a person can distinguish differences in the
> tens of cycles (OK: Hertz.) Personally I don't think so. I THINK you would
> want crystals as perfectly matched as possible... some of you crystal
> filter gurus can answer that. But overall as to this idea as a method, I
> don't think so. It NEVER hurts to ask Tim. How else are we going to learn.

Attemptng to measure each crystal by ear using just a receiver is, as Ed
says, not going to work well. However, if you wish to match crystals,
then you can build two identical oscillators, use one as a reference
and listen to the beat note between the two in your receiver. You can
accurately detect a beat note below 1Hz and probably above 50 Hz. I'd
run the oscillators on the bench and tune the receiver for reasonable
pitch - then listen to the beat note in the pitch.

I've done this many times to calibrate 10MHz oscillators against WWV,
with excellent results.

Dana K6JQ

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