Hi Let’s back up a bit:
The input to an ADEV calculation is a record of phase (time between wide spaced edges). Often this is from a PPS output on a device. It could equally well be from 10 MHz edges spaced a count of 10,000,000 edges apart. The first part of the formula takes the difference between adjacent samples. The next step puts that difference into a standard deviation calculation. If you are starting with something else, then you likely are not calculating ADEV. Bob > On Dec 3, 2018, at 11:21 AM, Mark Goldberg <marklgoldb...@gmail.com> wrote: > > I have looked at it multiple times and so far cannot see a discrepancy. The > ration of the ADEVs for the two sample rates is very close to 2 for a wide > range of Tau in the 10-200 sec range. That can't be a coincidence. It's > between 2 and 3 for higher Tau but that may be due to temperature changes. > > Basically, the Perseus SDR, clocked by my Bodnar GPSDO is sampling the 10 > MHz from my TruePosition and using the DDC to down convert to 48 kHz. I > then do either a 32768 or 262144 point FFT, resulting in window times of > 0.6816 or 5.453 sec and use a built in function in Spectrum Lab that as I > understand it interpolates the peak frequency from the highest two bins. > That calculated peak frequency is saved every 0.6816 or 5.453 seconds. That > data is fed to Timelab. > > I could do the same size FFT for both and decimate the input by 1 and 8 > respectively, which should result in the same FFT window time and check > that. > > I'm scratching my head here. > > Regards, > > Mark > > > On Mon, Dec 3, 2018 at 6:28 AM Bob kb8tq <kb...@n1k.org> wrote: > >> Hi >> >> ADEV is pretty well documented and the results should *not* be dependent >> on the >> sample rate. The proper approach to dropping the sample rate is decimation >> of the >> data. I think you may want to look at the way you are doing ADEV. >> >> Bob >> >>> On Dec 3, 2018, at 12:30 AM, Mark Goldberg <marklgoldb...@gmail.com> >> wrote: >>> >>> I ran them again today and the results are almost identical. The slower >>> sample rate still shows a lower ADEV. I am not sure what the algorithm to >>> determine the peak frequency is but it is described as a linear >>> interpolation between the two highest peaks on the FFT. I could see how >>> that could be subject to math errors. For the slower sample rate, the >>> frequency bins are smaller. I have not researched how all this could >> affect >>> the peak frequency and possibly introduce noise (or by truncation remove >>> small amounts of noise). >>> >>> I will run it a few times in the next few days and will also try to move >>> the antennas to a location with lower multipath. >>> >>> Thanks for the suggestions, >>> >>> Mark >>> >>> >>> On Sun, Dec 2, 2018 at 2:16 PM Bob kb8tq <kb...@n1k.org> wrote: >>> >>>> Hi >>>> >>>> Looking at the data, I’m guessing the slower sample rate was done last. >> If >>>> so, >>>> you may not be letting the GPSDO’s “warm up” long enough. Most designs >>>> take days (if not weeks) to get to their ultimate stability. >>>> >>>> Bob >>>> >>>>> On Dec 2, 2018, at 11:16 AM, Mark Goldberg <marklgoldb...@gmail.com> >>>> wrote: >>>>> >>>>> I broke down and drilled a couple holes in the wall and moved the >>>> antennas >>>>> for both GPSDOs outside with a better view of the sky, but still >> somewhat >>>>> shielded by the house and a metal RV cover. The number of sats is way >> up >>>>> and the TruePosition is in normal mode most of the time. The ADEV is >> not >>>>> improved and actually measured worse. I took data for twice as long at >>>> two >>>>> sample rates, 0.6816 sec and 5.453 sec. The ADEV from the slower sample >>>>> rates is lower, possibly due to the measurement method, but they all >> are >>>> in >>>>> the same order of magnitude. I've named the Heather screen captures for >>>> the >>>>> inside and outside locations and shown one combined Timelab capture. >>>>> >>>>> Regards, >>>>> >>>>> Mark >>>>> >>>> >> <TruePos_Outside_Ant_Heather.png><TruePos_Inside_Outside_Compare_Ant_Allan.png><TruePos_Inside_Ant_Heather.png>_______________________________________________ >>>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>> >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@lists.febo.com >>>> To unsubscribe, go to >>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>> and follow the instructions there. >>>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@lists.febo.com >>> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>> and follow the instructions there. >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.