Tom, Thanks for the explanation of clock ensembles. That answered a few questions I've had for a while. Regarding your comments on collecting raw time data from GPS and post processing it. Can you provide any reference info, links, etc. with more detail on that topic? Clearly I'd need a GPS that outputs the proper raw messaging and the software for processing it. I'm somewhat familiar with the techniques involved to improve GPS position data, but hadn't thought about it as much for timing.
Thanks, Rodger -----Original Message----- From: time-nuts <time-nuts-boun...@lists.febo.com> On Behalf Of Tom Van Baak Sent: Sunday, March 17, 2019 3:00 PM To: Discussion of precise time and frequency measurement <time-nuts@lists.febo.com> Subject: Re: [time-nuts] Frequency Ensemble > Hi Everyone,I like to know if it possible to run let say 10 GPSDO, 16 > Rb clock together and take the average to control 1 "master clock" and have better stability ? > like what BIPM or NIST doing. > I have search about ensemble system but I have no idea how much > advantage I get from some clock that I already have.Thank You Anton Anton, The rule-of-thumb is that, *under the right conditions*, N clocks will perform sqrt(N) better than 1 clock. So yes, NIST, USNO, PTB, BIPM -- all the big boys -- use ensemble techniques. But the key is that they mostly use cesium clocks, not OCXO or Rb clocks from eBay. Laboratory cesium standards don't suffer from frequency drift. The other key is that the clocks are independent. Under these conditions one can obtain sqrt(N) advantage. The problem with using cheap OCXO or Rb clocks is that they drift, and this drift may depend on make / model / environment; all of which are possibly common mode for you. This means the full sqrt(N) assumption is likely not valid. The problem with using GPSDO is that they are not independent clocks. In fact, they aren't clocks at all: they are just noisy radio receivers, implementing "time transfer" from the USNO GPS master clock, which is related to but not equal to UTC(USNO) which is related to but not equal to UTC itself. There's a lot of common mode error amongst a set of GPSDO. This means the full sqrt(N) assumption is likely not valid. Those who use GPS for highest accuracy tend not to use GPSDO. Instead they just collect raw timing information and post-process it some hours to weeks later. That is, they want to know what time-it-was-precisely rather than what time-it-is-approximately. A GPSDO only does the latter. /tvb _______________________________________________ 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.