As usual I cannot refrain to make my mistake: seconds for minutes... yes, it is 13 minutes not 13 hours.
On Sun, Dec 2, 2012 at 3:54 AM, Bob Camp <li...@rtty.us> wrote: > Hi > > > On Dec 1, 2012, at 8:13 PM, saidj...@aol.com 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, > > mag...@rubidium.dyndns.org 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 -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > 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. > _______________________________________________ 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.