Hi One Hz at a GHz is a one ppb. One ppb is one ns / sec. UHF TV is close enough to 1 GHz to simply call it 1 GHz.
1 us is 1,000 ns, so a 1 ppb offset will zero out the error in 1,000 seconds. That's roughly 20 minutes. All this from Bob, who just did the ms / us typo less than a day ago. Bob On Dec 1, 2012, at 9:17 AM, Azelio Boriani <[email protected]> wrote: > Here in Europe the use of GPSDOs has dramatically increased with the > transition to the digital TV broadcasting. The single frequency network > (SFN) mode of transmission requires the presence of a time and frequency > reference. The ETSI has a Technical Report (TR101-190) where the maximum > time and frequency error is stated: + or - 1uS for the time (PPS) and 1.1Hz > for the highest carrier frequency. The 1.1Hz max error for the frequency > binds the maximum recovery speed for the PPS. The UHF highest carrier is > 858MHz so that the 10MHz max frequency error is 0.01282Hz that is 1.282nS > for every second. To recover, say, 1uS, you need 12.8 hours. Recently > (April 2012), our national broadcaster (RAI TV) research lab (RAI CRIT) has > published an article in his technical magazine (Elettronica e > Telecomunicazioni http://www.crit.rai.it/eletel/ ) about how to test GPSDOs > for the SFN use. They state that the maximum time error, above which the > PPS recovery can be made with a phase jump, is 5uS but they forgot that to > recover 5uS without phase jumps at 1.282nS/S speed is 2 days and 16 hours! > > On Sat, Dec 1, 2012 at 11:17 AM, Charles P. Steinmetz < > [email protected]> wrote: > >> Hal wrote: >> >> I can see two ways to recover. One is to jump the 10 MHz clock by 10 >>> cycles. >>> The other is to adjust the frequency so that the PPS slews back to >>> on-time. >>> >>> The first approach gives you a second with the wrong number of cycles. >>> The >>> second approach has your clock frequency off for a while with a trade off >>> between how far off and how long it's off. >>> >> >> Both the TBolt and HP38xx default to the second method you describe, and >> both can be manually forced to jump to the nearest cycle (TBolt = "jam >> sync," HP = ":SYNChronization:IMMediate"), which gets the PPS within 50 nS. >> At that point, they revert to the first method and do the last <=50 nS by >> adjusting the oscillator frequency. >> >> The TBolt allows you to program a "maximum frequency offset," which seems >> as if it should establish a limit on how fast it can correct the PPS, but I >> have never seen one come anywhere near the default maximum offset. The >> TBolt also allows you to set a "jam sync threshold," which seems as if it >> ought to make the unit jam sync automatically when the threshold is >> exceeded -- but I've never seen one do that, either, even when set to "fast >> recovery." So far as I have seen, jam sync only occurs manually. >> >> Best regards, >> >> Charles >> >> >> >> >> >> >> >> >> >> >> _______________________________________________ >> 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. _______________________________________________ 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.
