I should have said warm start, not cold. I was referring to the code, not the oscillator. So tell me, the OCXO is warm, there's no previous EFC information to draw upon, and the oscillator is off-frequency by more than can be measured with, let's say eight timer bits. What do those early measurements tell me, and which direction from midway should the EFC be adjusted?
That's why I suggested a timer. Certainly, the delay chosen for a cold start would be excessive for a warm start, but I'm assuming that the GPSDOs we're discussing are not used in life-and-death circumstances where every second of unavailability is critical. Whenever you power up -- warm or cold -- you wait (probably ~ 5 minutes) for availability.
Using the PPS to discipline the oscillator during warmup may seem like a good idea. However: (i) it will not be disciplined to useful time-nuts standards both because it is drifting and because the frequency is being set by the noisy, jittery GPS PPS signal. But much worse, (ii) if the loop is fast enough to track the oscillator as it warms up, it is almost certainly too fast to give best performance at low to medium tau when the oscillator is warm, because the noisy, jittery PPS will be contributing to stability at tau where the nice, quiet OCXO should be in charge.
Precision takes time. Time nuts can't afford to be impatient. Best regards, Charles _______________________________________________ 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.
