Hi
On Dec 1, 2012, at 8:13 PM, [email protected] wrote: > Hi Magnus, > > yup, at the levels we are interested in, a prefix or two sometimes doesn't > make any real difference :) > > Most of the time typical GPSDO's won't ever drift out of a say +/-100ns > window. If they do, then the antenna must have been shot off by someone, or > something else must have gone horribly wrong. > > Just for fun I attached two phase correction examples from a FireFly-IIA, > and a CSAC GPSDO. Both were essentially brand new and not yet calibrated > when turned on, and thus you can see a large EFC variation over the first 15 > minutes or so as the frequency stabilized. > > Then you can see the phase stabilize slowly, this takes about 1.2 hours for > the FF-IIA with a much more aggressive loop setting, and about 3 hours for > the CSAC GPSDO. > > The most perplexing fact for me is that while you can clearly see the exact > point at which the phase has stabilized, you cannot really see any > corresponding change in EFC behavior at that time. You can see a large EFC > voltage > change initially as the frequency stabilizes after power-on, but then it > goes into the noise floor. This shows that the EFC corrections for phase > error are essentially smaller than the proportional noise floor of the loop! > Driving an integrator is never an easy thing. Watching EFC and looking at phase indeed watching the loop drive an integrator. > The maximum phase error in these plots was about 100ns for the CSAC, and > 230ns for the FF-IIA. Here we can see that the FF-IIA has a much more > aggressive loop approach (~5x more gain on the phase correction). Since the > CSAC > is an atomic clock we can increase the time constant quite a bit and make > the loop much less aggressive. > > bye, > Said > Bob > > In a message dated 12/1/2012 14:39:58 Pacific Standard Time, > [email protected] writes: > > One can also wonder if the limit is relevant, as you are about to > resolve a rather catastrophic situation where you already cause > interference, so moving out of it quickly should be first priority and > only when back to reasonable time-error would it be relevant to obey > frequency error limits. > > The transmitters and the recievers would be able to follow, as they have > large enough bandwidth for it. > >> But if you set the loop parameters more aggressively to 1ns/s as in your >> example, it would take less than 20 minutes to correct 1us.. Not 12hrs. >> Unless you meant to say ms? > > What's a off by one prefix among friends? > > But still, one has to be careful. > > Cheers, > Magnus > > > <phase_corrections.zip>_______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
