[Test-Equipment] crystal checker

[Chris Trask]

>
> > Would there be any interest in a full-blown crystal
> > test set for measuring the crystal motional parameters
> > (Rx, Lx, and Cx)? 
>
> Yes!
>

     Okay, I've had a few positive responses to that.  I'll take some time and write up a formal document for this.  I've  been mulling over a much more detailed article for QEX or elsewhere, and I'd like to send it off to Wes Hayward to see if he'd like to publish it in QST.

     It actually took me a while to understand what was so obviously wrong with the G3UUR circuit.  I knew that the circuit was parallel-resonant simply because it was a Colpitts oscillator, but his claim that it was series-resonant just didn't jive.  The trick was that he was loading up the holder capacitance (Cs) with a pair of 470pF capacitors in the feedback network, forcing the parallel-resonant frequency to be considerably closer to the parallel-resonant frequency so that they were approximately equal.  That's a nice, cost-effective approach if you're not overly concerned with being precise, but it can be a serious issue when designing narrow-band crystal filters.  




Chris

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