Tom, i believe that Bruce as well as me is always referring to what the receiver CAN do i.e. not the raw but always the sawtooth corrected signal. That is indeed 2 ns (1 sigma).
> Don't mislead yourself. At 1 s you are limited by GPS > 1PPS noise. Having a better TIC doesn't fix this. If your > GPS noise is 2e-9 at 1 s you don't really need a TIC > that is good to 5e-10 at 1 s. So the gain isn't as useful > as you might think. Thank you for clarifying this again! While i have been referring to the measurement apparatus's noise floor for which my statements are correct, one might indeed get into believing that every increase in resolution leads to a increase in performance in a GPSDO. Clearly once that you are below a certain point the GPS's jitter is the limiting number. I second Bruces's opinion about what is an overshot or not. When ps reolution is ready available then why not use it? I attach a online output from my DIY GPSDO from a few minutes ago that shows the M12+'s signal properties when measured with abt. 110 ps resolution against a FTS1200. The yellow line reperesents a prefiltered version of the sawtooth corrected values (blue). The filter time constant is 1/3 of the loop time constant as in a PRS-10. The yellow values are the ones to feed the regulation loop. What I wanted to explain is the Shera concept noise floor is a factor 20 above what a modern receiver can deliver (again inc. the sawtoth correction). And yes, you are right: There were different numbers when this concept was thought out! And exactly because different number were there when this concept was thougt out I am going to ask why people still built it today. Best regards Ulrich Bangert, DF6JB > -----Ursprüngliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Tom Van Baak > Gesendet: Freitag, 15. Dezember 2006 08:23 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] LPRO-101 with Brooks Shera's GPS > locking circuit > > > > Tom > > > > A TIC with 0.5ns jitter at 1 second isn't actually too much > in the way > > of overkill when the PPS signal has 2ns of jitter. > > Bruce, > > Can you clarify about the jitter, though. The TIC jitter > that was quoted (500 ps) is the single-shot resolution > for the 53131A. The "2 ns" M12+ jitter is an rms value, > no? The short-term or "single-shot" M12+ jitter, if you > could call it that, is more like +/- 20 ns. Averaging it, > over many minutes, gets you below 10 ns. Also the > sawtooth correction helps even further but that isn't > being done with Shera's board. > > Maybe we're all agreeing even if with different words. > > /tvb > > > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts >
AOSChart.pdf
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