Björn, thank you for the link! Looks very interesting!
Regards Ulrich Bangert, DF6JB > -----Ursprüngliche Nachricht----- > Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Im Auftrag von [EMAIL PROTECTED] > Gesendet: Donnerstag, 14. Dezember 2006 13:30 > An: Discussion of precise time and frequency measurement > Betreff: Re: [time-nuts] Best GPS 1PPS Accuracy > > > Ulrich, > > +-3 sigma is 99% on a gaussian distribution. > > If you want to look at other algorithms on this topic, here is one: > > http://www.control.isy.liu.se/books/adfilt/ > > br, > > Björn > > On Thu, December 14, 2006 12:55, Ulrich Bangert said: > > Hello Said, > > > > from my own experience in detecting and removal of outliers i can > > asure you that it is a challenging and ambitious task in > statistical > > math. I fear you expect too much from a receiver's TRAIM > firmware to > > compute the necessary statistic math on a pulse to pulse base. > > Nevertheless you can do it on your own if the microcontroller that > > compares the LO to the GPS's 1pps has enough RAM and > processing power. > > > > It involves computing the MEDIAN over a number measurements > (say 60) > > to get a reliable estimate of the measurement's MEAN value in that > > time. Note that the normal MEAN computation is susceptible > to outliers > > while the MEDIAN is not. On the other hand computing the MEDIAN > > involves sorting the measurements in ascending order, much > more stuff > > than simple MEAN adding/dividing. Once you have the MEDIAN of your > > measurements you can compute the distances between the single > > measurements and the median. But in contrast to the simple STANDARD > > DEVIATION which is susceptible to outliers itself, you now > compute the > > MEDIAN over the distances between the measurements and > their MEDIAN to > > give you something that is called the MAD (MEDIAN ABSOLUTE > DEVIATION. > > As the STANDARD DEVIATION the MAD is a measure of the witdh of the > > measurement's distribution in the sense of a 'sigma' but not > > susceptible to outliers. Once you have that number you can easily > > decide whether the last measurement is within or without a range of > > say +/- 5 * sigma. I guess +/- 5 * sigma resembles 99% of normal > > distributed values, so you are on the safe side to throw > away anything > > outside +/- 5 * sigma. Note that you have to perform the > above steps > > for every new measurement, i.e. every second removing the oldest in > > your data buffer and adding the latest measurement to you > data buffer. > > It can be done and i do so in my DIY GPSDO but actually it needs > > exactly this complexity. > > > > Best regards > > Ulrich Bangert, DF6JB > > > >> -----Ursprüngliche Nachricht----- > >> Von: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] > >> Im Auftrag von [EMAIL PROTECTED] > >> Gesendet: Donnerstag, 14. Dezember 2006 01:56 > >> An: [email protected] > >> Betreff: Re: [time-nuts] Best GPS 1PPS Accuracy > >> > >> > >> Hi guys, > >> > >> slightly off-topic, but has anyone done stability tests > with the m12+ > >> or M12M when the antenna goes bad in TRAIM-enabled mode (e.g. > >> less than 4 good sats > >> being received by i.e. disconnecting the antenna)? > >> > >> I see that the 1PPS output goes away only after about 5 or so > >> additional pulses have been generated, so these 5 pulses are > >> "free-running". > >> > >> These pulses are somewhat inaccurate, and I am wondering if anyone > >> has done a max/min analysis on the errand pulse's offsets? > >> > >> I wonder if the TRAIM limits can be set to say +-50ns > effectively to > >> kill these pulses and improve overall accuracy? > >> > >> I know lot's of folks run the M12 TRAIM limits at 1us, that seems > >> excessive on a receiver that is supposed to do 10ns > 1-Sigma, doesen't > >> it? ... > >> > >> Thanks for your feedback, > >> Said > >> _______________________________________________ > >> time-nuts mailing list > >> [email protected] > >> https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > >> > > > > > > _______________________________________________ > > time-nuts mailing list > > [email protected] > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > > > > > _______________________________________________ > time-nuts mailing list > [email protected] > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
