On 29 Nov, 2012, at 02:32 , Charles P. Steinmetz <charles_steinm...@lavabit.com> wrote:
>> This is a classic crystal jump. The crystal changed its frequency magically >> from one second to the next and the software compensated for it > > Here is another example of a 3805 having a bad moment. For just about two > minutes, it reported a phase jump of nearly 3 uS and then immediately fell > back nearly to its previous baseline, settling to the baseline in about an > hour and not requiring any longer-term change of the EFC voltage. This does > not look like a typical crystal frequency shift to me, but I cannot rule that > out. It looks more like what I'd expect to see if I set the cable delay to 3 > uS for 2 minutes, then back to 0. I think I would be more likely to call this one, where the crystal jumps to another frequency for a while and then jumps back to about what it was, a "classic crystal jump". I've seen this before, though not as large as the change you show. I hear these raise hell when they try to use PTP to transmit telecom-quality timing over asynchronous ethernet because it is hard to run a PTP control loop tight enough (i.e. at a high enough data rate) to correct that before it does damage. I think the other problem, with the crystal jumping to another frequency and apparently staying there (I'm assuming it hasn't jumped back), could have a broader range of causes. Dennis Ferguson _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
