Thankyou to all who responded. It looks as if 2 parts in 10^12 is about what can be expected - certainly much better than the 1 part in 10^9 available from a typical double ovened quartz crystal oscillator barefoot. Cheers!...............................................................................................................................Donald Brett Collie
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free. www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Fri, Sep 11, 2020 at 1:15 AM Bob kb8tq <[email protected]> wrote: > Hi > > Maybe a good idea to “back up” a bit here: > > The most commonly plotted data for the performance of a GPSDO is ADEV. > Very simply put, to do ADEV you take a series of readings at a specific > time > spacing ( called tau ). The delta frequency from one reading to the next > is then > computed. You take the standard deviation of that “delta” information. > > What you are looking at is the “good guess” at what the frequency will be > in the > next time slot, based on what it is in this time slot. This may or may not > be what > your system / measurement instruments are looking as a. spec. > > The big reason ADEV exists is that it is convergent. As you take more > data, the > results don’t move all over the place, they converge to a single value. > Measure today, > then measure tomorrow, you get pretty much the same number. > > You might want to know what the maximum frequency error compared to > “absolutely > correct” is in your 10 second time period. This is a measure that is > non-convergent. The > longer you collect the data, the bigger the number gets. Measure for an > hour and you > get a different number compared to measuring for a day. Measure today / > measure > tomorrow and you may get dramatically different results. > > This is not to say that nobody ever can know what the frequency is. Only > that “max” is > not a good limit for this sort of random fluctuation. Again, this is what > drove the guys > at NIST to come up with ADEV back in the 1960’s. It’s what keeps us using > it as a > means of comparison today. > > Bob > > > On Sep 9, 2020, at 7:04 PM, donald collie <[email protected]> > wrote: > > > > Can any list member please tell me the "accuracy" that can be expected > from > > a typical GPSDO > > over, say, a 10 second interval? I have several measuring instruments > > connected to my Trimbal GPSDO, and would like to know what to expect. At > > the moment I am guessing about 1 to 2 parts in 10^12. > > > Thankyou,................................................................................Donald > > Brett Collie > > > > < > https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail > > > > Virus-free. > > www.avast.com > > < > https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail > > > > <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
