> 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.
You might have an intermittent solder joint or component lead that's being flexed when you touch various points with the probe. Does a plastic alignment tool cause the same behavior? Or, more likely, there's so much loss in the circuit due to aging/component failure that it won't restart oscillating on its own without going through a power-up cycle. -- john, KE5FX _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
