Thursday, January 28, 2010

Frequency unknown

I recently bought a batch of crystals on eBay. They are from early 2m FM crystal controlled transceivers, some are receive crystals and some are transmit crystals. They have the 2m frequency stamped on them, not the actual frequency of the crystal. Because I don't know what radios they were from originally I do not have the remotest idea what their real frequencies are.

I Googled up "crystal test oscillator" and breadboarded the first circuit I found, a Colpitts oscillator, but it didn't appear to work. I tried several crystals but could not detect any oscillation. I tried one of my HF QRP CW crystals and I couldn't receive a signal from that either, so obviously my oscillator was no good. I didn't want to build something permanent as this is probably the only occasion I'll ever need to use it. But I'm a bit stumped as to what to try next.

As I'm going to be tied up for the next couple of days setting up the new shack computer I'll probably put the crystals back in the junk box for now. But I really need to find out what they are as a future project depends on them. I had to buy more crystals than I needed because of the way they were auctioned on eBay, so I want to get rid of the ones I don't need. But I'd prefer to sell them as tested and to be able to tell buyers the frequency.

Any suggestions?
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