[time-nuts] "GPS once a day issues" ?

Bob Stewart bob at evoria.net
Sun Oct 19 22:01:12 EDT 2014

Hi Bob,  (Yahoo let me down again and I responded only to you.  Here is my reply again.)

OK, it sounds like something that would not be clearly noticeable with the 
equipment I have.  I haven't run many multi-day tests, so that's another handicap on this end.  Still developing and testing, but things are 
looking better than the last time I spoke about my unit.



 From: Bob Camp <kb8tq at n1k.org>
To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Sunday, October 19, 2014 8:50 PM
Subject: Re: [time-nuts] "GPS once a day issues" ?


The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite  geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing. 


> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob at evoria.net> wrote:
> Hi Bob Camp,
> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
> Could I ask you what you meant by these "once a day issues"?  Was this a general comment, or was it about something specific?  As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
> Bob - AE6RV
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