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Crystal Oscillator Stability

First of all, I'd like to thank everybody who sent
me data and suggestions on improving the stability
of the oscillator on my DEM S-band convertor.

I ordered and installed one of the PTC thermistors,
soldering it to the crystal and feeding it with
a 9-volt regulator.  I also fitted a lovingly hand-crafted
hollow styrofoam cube over the crystal for insulation.

After running it for couple of weeks, I observe
a positive change of frequency with temperature:
Moving the convertor from my shack to the attic
(and back a couple of times) results in a ~3 kHz
frequency shift for a ~40 degree F temperature change.

This is about .05 PPM per degree C,
or 5*10^-8 per degree.  

Does this sound reasonable for an oven-ized crystal?
Would there be any worthwhile way to further improve
the stability, without oven-izing the entire unit?
BTW, my circuit has the RF choke across the crystal,
and uses the RSK-1 transistors.


Doug Braun

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