So MAYBE one could improve the temperature stability of the TCXO
environment. First step, surround the TCXO with a block of Dow blue
board (or white or gray). That will slow the effect environmental
changes reaching the TCXO. That worked on the calibrator crystal in my
Collins 75S3C 40 years ago (a coat of aluminum foil helped keep tube
heat away) to let me get to 1 ppm in a FMT in the 70s. Then one can add
a bit of crude temperature control inside the foam. The simplest thing
is a positive temperature coefficient thermistor. Say at 30 or 40 degree
C. The temperature chosen needs to be above the highest ambient you
expect frequency stability. This is a commonly applied technique for
stabilizing local oscillators in VHF/UHF and low microwave transverters.
Digi-Key has sold a quarter inch diameter positive temperature
coefficient thermistor that when connected to 12 volts (and it should be
powered independent of the radio power) heats up fairly quickly and
holds temperature of the crystal within a smaller variation that room
temperature. That gives the Temperature Compensation of the XO less work
to do and the frequency should be significantly more stable.
Try D-K KC001P-ND for 30 degree C or KC002P-ND for 40 degree C. The work
for me.
73, Jerry, K0CQ
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.
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