> Hi Antonio, Tom, > > recently I had to unplug my PRS10 Rb from GPS for about 3 days. It drifted a > couple 100ns in that time frame. > > When I plugged the GPS 1PPS back in, I saw a significant frequency error of > a couple of parts to the E-10 while the PRS10 was shifting the 1PPS back > onto > UTC. > > Pretty bad for a Rubidium I thought. > > For such a large phase error I would have expected the PRS10 to just reset > the 1PPS rather than drift it.
Said, But why expect a reset in this case? This would then mean a sudden frequency change of 100 ns / 1 s, or 1e-7! So you have to ask what's worse: a sudden jump in the e-7 range or a gradual change in the 1e-10 range. Or, should it jump the 1 PPS and drift the frequency? Or keep the 1PPS and frequency in phase and drift them both? Or jump them both? Hard question. The answer is -- there is no right answer. It all depends on the design specs of the unit, or the needs of your application. Sometimes a jam sync is in order, sometimes an elevated but bounded drfit rate. If you're lucky, the GPSDO gives you an option whereby you can program your threshold; your "expectation". But internally every GPSDO has to make a decision about when to jump vs. when to drift. Whether it's hardcoded or programmable is the question. See section 5.1.1 of the Trimble Thunderbolt manual for a good example of how this can be done. /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.