Random noise or not, wouldn't a position error in a nav receiver cause a corresponding displacement of the 1PPS pulse?
Also there's a bit more to it than just minor noise. It's probably multipath, or perhaps even jammers passing on the freeway about a mile away. Whatever the cause, take a look at this screen capture of "foxtrotgps" over about 40 minutes of elapsed time. The red is the GPS movement around my house that I periodically mention. I judge it to be about 15 ft on the diagonal. Sometimes it is much much worse. Likewise I would expect the 1PPS to move by that amount. http://www.evoria.net/AE6RV/Nav/NavWander.png Bob >________________________________ > From: Chris Albertson <albertson.ch...@gmail.com> >To: Bob Stewart <b...@evoria.net>; Discussion of precise time and frequency >measurement <time-nuts@febo.com> >Sent: Sunday, March 23, 2014 9:24 PM >Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? > > >What you are seeing in position error is a random noise. There is no >pattern to it and it is not predictable. A sawtooth error is very >nice and regular looking. It's not "noisy" and can be predicted in >advance. Possition error is not at all like sawtooth. > >I think what you CAN do is look at the size of the error. Then you >adjust the gain on the loop control based of the measured error sigma. > > > > >On Sun, Mar 23, 2014 at 6:30 PM, Bob Stewart <b...@evoria.net> wrote: >> Hi Ignacio, >> >> Thanks for the response. I've got a UT+ in the parts box. But that's not >> the problem I'm trying to solve. I'm trying to make the best GPSDO that I >> can make using a nav receiver at the moment. Call it an obsession if you >> like. It's OK if I don't have corrections to the nanosecond for each PPS. >> But I can see the nav receiver wandering around; especially on cloudy days, >> (the antenna is in the attic, so that's about the best I can do for that) >> and it just seems to me that I should be able to do a general correction for >> nav position errors. Sorry if my naive posts are starting to get on >> people's nerves. >> >> Bob >> >> >> >> >>>________________________________ >>> From: EB4APL <eb4...@cembreros.jazztel.es> >>>To: time-nuts@febo.com >>>Sent: Sunday, March 23, 2014 7:35 PM >>>Subject: Re: [time-nuts] Nav Receiver Sawtooth Correction? >>> >>> >>>Bob, >>> >>>The sawtooth is generated by the granularity of the GPS receiver clock >>>not being synchronous with the recovered PPS. The receiver program can >>>calculate the correction to be applied to the next PPS and outputs it in >>>a message, bu only in timing receivers, this is not a useful thing in >>>navigation receivers and I think that it cannot be calculated using the >>>satellites' position, it is a receiver "defect". >>>Why don't you buy a timing receiver? An used Motorola Encore M12+ >>>timing receiver can be bought by $35 or less (ebay items 290656401551 or >>>301131583613. The seller is a known Time Nuts supplier). An UT+ or GT+ >>>even for quite less. >>> >>>Regards, >>>Ignacio EB4APL >>> >>> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > > >-- > >Chris Albertson >Redondo Beach, California > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
