Hi Bruce, > I read your paper in the AMSAT Journal and believe that an English > translation of this would be very informative to those who > cant read German.
Please allow me to ask: Did you get it from my homepage or did you have a printed version of it?? Best regards Ulrich Bangert > -----Ursprüngliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von Dr Bruce Griffiths > Gesendet: Sonntag, 29. Oktober 2006 14:37 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Allan Deviation -> moredata: GPS1PPS > against OCXO/128 > > > Ulrich Bangert wrote: > > Bruce, > > > > > >> If GPSDO did some statistical filtering instead of just blindly > >> accepting all PPS signals as valid and usable such dropouts > >> would cease > >> to be much of a problem. > >> There's no substitute for a a correctly engineered design with an > >> appropriate tracking loop bandwidth and statistical filtering > >> of outliers. A good crystal will drift very little over half > >> an hour or so when the > >> GPS derived PPS signal may be unreliable. > >> > > > > I have read lots of intelligent stuff from you in the last > weeks that > > makes you a brother in mind, but let me explicitely say THANKS for > > this one. > > > > I have been using robust statistical methods in my own GPSDO design > > since years now. Every new second I compute the median over some > > hundred seconds of past phase data and after that i compute the MAD > > (median absolute deviation) over the same period. The MAD is is a > > measure for the width of the statistical distribution as is the > > standard deviation. Unlike the standard deviation, is it completely > > insensible to outliers itself. 99% of "normal" data are within +/-5 > > MAD around the median so once you have performed the math > it is really > > easy to detect outliers. > > > > Since the algorithm needs a certain amount of RAM and sheer > processing > > power this is not easily done with single-chip-processors. > > > > Thank you for pointing at the fact that sometimes a certain > complexity > > of hardware and software is necessary to get a job done and > that the > > quality of a GPSDO cannot be measured in term of low&cheap > parts count > > as seems to be a quite common opinion. > > > > Best regards > > Ulrich Bangert > > > > > >> -----Ursprüngliche Nachricht----- > >> Von: [EMAIL PROTECTED] > >> [mailto:[EMAIL PROTECTED] Im Auftrag von Dr > Bruce Griffiths > >> Gesendet: Samstag, 28. Oktober 2006 23:46 > >> An: [EMAIL PROTECTED]; Discussion of precise time and > >> frequency measurement > >> Betreff: Re: [time-nuts] Allan Deviation -> more data: > >> GPS1PPS against OCXO/128 > >> > >> > >> kd7ts wrote: > >> > >>> Didier Juges wrote: > >>> > >>> > >>>> There are sudden increases in noise (bursts that last from > >>>> > >> seconds to > >> > >>>> minutes) on the plots I posted. > >>>> > >>>> I believe the sudden and drastic increase in noise at times comes > >>>> from > >>>> the GPS loosing lock. At the moment, I cannot hook up the > >>>> > >> computer to > >> > >>>> the GPS and verify, but I will do that later. > >>>> > >>>> > >>> -------- > >>> > >>> I have a Brooks Shera GPSDO that exhibited similar symptoms. The > >>> phase showed huge jumps around 4:00 - 4:30 every morning. The PLL > >>> loop might, or might not recover, but usually didn't. I > didn't have > >>> the time to spend troubleshooting, and we seldom ran tests > >>> overnight, so I just lived with it for more than 5 years. > >>> > >>> I retired recently and finally had the time to devote to > finding the > >>> problem. It was so easy, it is almost embarassing. I picked up > >>> another GPSDO system based on a Jupiter GPS engine and an Isotemp > >>> ovenized 10 MHz oscillator with EFC. It was the antenna I > purchased > >>> to go with this, that turned out to be the useful missing > piece of > >>> the puzzle. > >>> > >>> I swapped antennas between the two units to compare the > SS numbers > >>> reported by the Motorola UT+. They appeared to be about > the same, so > >>> I swapped them back. This continued for another week or so, and I > >>> exhausted all remaining possibilities. I swapped the two patch > >>> antennas again, but this time I let it run for a week. I never > >>> observed the problem during this time, so I replaced the patch > >>> antenna > >>> (cheap) with a Symmetricomm antenna that is commonly used on > >>> Cell sites. The system has been 100% for about 3 weeks now. > >>> > >>> I beleve the Symmetricomm antenna has much better filtering, and > >>> because it has an "N" connector, I was able to use a > longer cable, > >>> with lower loss and better mounting location. > >>> > >>> Watching the SS numbers reported by the UT+ did not provide any > >>> insight. They were generally between 43 and 47 and > tracking 8 with > >>> the patch antenna. I have been watching the numbers for about 2 > >>> weeks with the Symmetricomm antenna connected, and they > show between > >>> 47 and 52 and tracking 8. > >>> > >>> I can only speculate on the exact mechanism, but it > appears that the > >>> system is functioning properly. > >>> > >>> It is the station reference for 10 and 24 GHz transverters and a > >>> DSP-10 IF rig. > >>> > >>> We have 5 of these GPSDO units in the area, and all I ever heard > >>> was, "well mine runs just fine !" > >>> > >>> > >>> > >>> Mike KD7TS > >>> > >>> > >>> > >>> > >>> > >>> _______________________________________________ > >>> time-nuts mailing list > >>> time-nuts@febo.com > >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >>> > >>> > >>> > >> Good timing antennas have built in ceramic or equivalent bandpass > >> filters to minimise the effect of interference. > >> A patch antenna is not as satisfactory as a quadrifilar helix > >> or a choke > >> ring ground plane antenna for accurate timing purposes. > >> > >> If GPSDO did some statistical filtering instead of just blindly > >> accepting all PPS signals as valid and usable such dropouts > >> would cease > >> to be much of a problem. > >> There's no substitute for a a correctly engineered design with an > >> appropriate tracking loop bandwidth and statistical filtering > >> of outliers. A good crystal will drift very little over half > >> an hour or so when the > >> GPS derived PPS signal may be unreliable. > >> > >> Bruce > >> > >> _______________________________________________ > >> time-nuts mailing list > >> time-nuts@febo.com > >> https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > >> > >> > > > > > > _______________________________________________ > > time-nuts mailing list > > time-nuts@febo.com > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > Ulrich > > I read your paper in the AMSAT Journal and believe that an English > translation of this would be very informative to those who > cant read German. > > Bruce > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts