Crystal Oscillator

I currently have three: a really old optoelectronics Opto-7000 which I don`t use much, a newer Mitronics MIC-1028, and my most recent acquisition, a used Tektronics 2236 `scope purchased at Dayton 2009, which has a very handy frequency counter built-in. I was working on a recent project and found the Tektronics and theMitronics counters were annoyingly out ofagreement.

How to check the calibration So I built this 10 MHz crystal oscillator. There are a lot of crystal oscillator circuits if you search the internet, some of them amazingly complex. I wanted one that was simple, had no tuned circuits, and could be tweaked to get it on frequency. I use my shortwave receiver tuned to WWV at 10 MHz. I adjust C2 to zero-beat with WWV. This can most easily be heard when the tones are present, since mis-tuning makes the tones sound wierd. Once zero-beat, the frequency counter should read 10 MHz too. I found my Tektronics was spot on, and theMitronics needed adjustment, which was easy to do since the calibration trimmer was accessible through a small hole in the front panel. Since completing this project, I came across an interesting article on how to calibrate a counter (that has an internal 10MHz oscillator) without any extra gear (besides a receiver for WWV). Have a look at VE2ZAZ`s blog. It doesn`t work with my Mitronics counter, though, so it must use a different reference oscillator frequency.

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