A Crystal Checker (Oscillator and Buffer)

So today among other things, I decided to pull out the crystals and start playing with simple crystal oscillators buffers and perhaps even at a later stage, expand on this to VXO and Super VXO’s and make myself a pretty simple rock bound rig with some frequency agility.

So i digress, today i knocked up a simple collpits oscillator and buffer to be used as a crystal checker. We all have crystals we cannot read the value of, so having a simple oscillator to stick them into to find out their frequency, is a handy thing to have and being simple, you can knock one up in a lazy afternoon and keep yourself busy for a while.

 

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So i laid the board out ans routed up a board. There is an error in the schematic. The value of the 470 capacitors should be pf (Pico Farads) not nf.

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The board was assembled and smoke tested. Ran into a little issue at this point, no output from the buffer. The oscillator was doing its dance and making nice sine waves, but the buffer was not playing its part and buffering. After a lot of hair pulling, asking questions of much smarter people than me and getting some good and some not so helpful answers, I ripped the DC blocking cap out, measured it and found it was short to ground. Replaced said cap, buffer fires up and strts buffering.
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Output of an 80m colour burst crystal, showing nice harmonic content as the oscillator is being driven a little too hard and going non linear.


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Output from a 10MHz crystal i bought to use as an IF filter in a Superhet, nice and clean and no harmonics present. Was a good little bit of fun, next I will have to build another and turn it into a VXO and then a Super VXO and eventually a rock bound rig.

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