Certainly. However I was addressing only the measurement capabilities of the timer with regard to its width, not the overall operation of the system.
> On Apr 10, 2014, at 15:52, "Tom Miller" <[email protected]> wrote: > > Don't you also need to wait for the GPS at first power up? > > ----- Original Message ----- From: "Charles Steinmetz" <[email protected]> > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Sent: Thursday, April 10, 2014 3:31 PM > Subject: Re: [time-nuts] First success with very simple, very low cost GPSDO > > >> >>> 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. _______________________________________________ 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.
