Ulrich Bangert wrote: > 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 > > Ulrich
I just used the link you posted a few days ago. Bruce _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts