> Btw, is anybody using this technique nowadays, like heated frequency
> sources? It would be much easier now, with peltier elements and some
> kind of integral regulator. I have seen audio amplifier IC used for
> this regulator somewhere.

I think crystal ovens are still a good idea for ultimate stability. You
can temperature compensate a crystal oscillator, but it's probably better
to just hold it at a constant temperature. I remember seeing a "clamp on
crystal oven" years ago that was, I think, made by CTS. It was a PTC
thermistor that attached to the crystal. Put a fixed voltage across the
thermistor and it self heated the crystal to a fixed temperature.

Another constant temperature device is the LM399H voltage reference. I
think it's good for something like 0.5ppm/K . It's probably one of the
most stable references around. It heats the reference diode to some
constant temperature.

Harold


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