[time-nuts] Ancient OCXO in scope calibrator.

[David C. Partridge]

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

Cheers
Dave