[Milsurplus] Crystal tester

[hwhall at compuserve.com]

I remember encountering that CMOS design but if I recall correctly the text that was with it indicated C1 & C2 & Rs had to be selected for the xtal range to be used.https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/oscillator-osc32a.gif
I haven't given that one a breadboard try yet.

WayneWB4OGM

-----Original Message-----
From: Al Klase <ark at ar88.net>
To: milsurplus <milsurplus at mailman.qth.net>
Sent: Sat, Aug 10, 2019 10:48 am
Subject: Re: [Milsurplus] Crystal tester

 Gang,
 
 Crystal testers have been of interest to me for a long time.  There are a lot of published circuits out there, and there have been some actual products over the years.  Most of these work just fine for crystal in the MHz range, but don't work well with things like 100KHz calibrator xtals or military FT-241's that are the the 300-500KHz range.
 
 Most modern devices implement crystal oscillators by biasing a CMOS logic gate/inverter into analog operation by connection a 1-2 meg resistor from input to out put, and connecting the crystal like so:
 
  
 This Texas Instruments app note dopes out the whole matter:  http://www.ti.com/lit/an/szza043/szza043.pdf
 
 Basically, all one has to do is change the value of Rs to accommodate different frequencies.  E.g. 50K ohms for 100 KHz rocks.  I started in on this a while back and had encouraging results with a 100K pot for Rs.  (can't find my breadboard. :-()  I intend to add some sort of analog meter to the output of the oscillator gate to indicate activity, and buffer the output with the other devices in the IC to and output connector and possibly a $10 counter module from E-bay.
 
 Too many projects!
 Al
 
 -- 
Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

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