On Mittwoch, 12. August 2020 13:23:57 CEST Tobias Pluess wrote: > On the picture `gpsdo_180_210.png` one can see the last 30 hours of my > measured data. During this time, the DAC value need to change only by 9 > counts. I think the DAC value has a slight trend to go lower and lower, > this is perhaps because my OCXO was new and is still a bit aging. Phase > error stays within +/-15ns during the whole time!
TimeLab can tell you the linear drift from the imported data. > As I still don't have a proper DMTD system or anything similar which allows > me to `quickly` estimate the stability of my device, I made some > experiments and imported my logged data int Timelab. This can be seen in > the picture `timelab_estimated_from_dac.png`. The blue curve results when I > analyse the phase error. As expected, since this is essentially the > performance of the 1PPS signal, the curve goes lower and lower. (I imported > this data as "phase difference" and scaled it with 1e-9). > The pink curve results when I let Timelab analyse the DAC values. This idea > is actually from a colleague on this list. It assumes that the OCXO is > perfectly stable and the only instability comes from the DAC being > disturbed by the 1PPS noise. To analyse this, I imported the data as > "Frequency Difference" and scaled it appropriately (scaling factor is > 7.6e-12 as I have approx. 5 to 6Hz tuning range of the OCXO per 16 Bits). I > am not sure how accurate this estimation will be, but if it is only close > to the reality then it appears that my GPSDO has a stability in the range > 1e-12. According to John's comparisons here: > > http://www.ke5fx.com/gpscomp.htm > > this would mean it is slightly better than a BG7TBL and quite a bit worse > than a Tbolt with 10811A oscillator. The DAC analysis tells you mainly how much "instability" the regulation causes for a given tau. The GPSDO output can not be better than this value. Typically, it's worse than the DAC ADEV. I've been doing some simulations with TvBs GPSDO simulator a while ago (might have posted some graphs here, cannot quite remember), the DAC ADEV (or MDEV) starts to influence the OCXO performance when they become close. > Comments welcome. I hope I get my two Rb standards soon and can then do > some DMTD tests. Looking forward to seeing some actual measurements! > > > Tobias > HB9FSX > _______________________________________________ > 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.
