[time-nuts] Ancient OCXO in scope calibrator.
David C. Partridge
david.partridge at dsl.pipex.com
Tue Sep 9 14:19:39 EDT 2008
Following the good advice I received about increasing the value of the
trimmer capacitor, I replaced the trimmer which was originally 3-12pF, with
another one which was 2-22pF.
This has given the additional adjustment range to allow me to pull the
crystal to meet the specification.
It's not mega-stable, varying between 9.9999619 MHz to 10.0000232 MHz over
the course of a minute or so as the thermostat cycles, but certainly within
the 10ppm specification and varying up and down by about 6-7ppm. This is
before the full 2 hour warm up period is complete, but I don't things will
change much over the next 45 minutes or so. The stability seems to be
improving as the warm up continues which is good.
I may be able to tweak it so the variation is more evenly balanced around
10.0000000 MHz, but the trimmer adjustment is pretty sensitive.
Still don't understand why probing with a 10Meg, 1pF load kills the
oscillation stone dead until the next power cycle.
Thanks to all
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