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

John C. Westmoreland, P.E. john at westmorelandengineering.com
Mon Oct 20 07:31:44 EDT 2014


Bob,

You mean the Sun, correct?

Regards,
John
 On Oct 20, 2014 4:16 AM, "Bob Camp" <kb8tq at n1k.org> wrote:

> Hi
>
> Yes, but there’s this large object in the sky that modifies the ionosphere
> as it travels in a “about one a day” track. It appears to be coming up just
> about now, but I do need more coffee to be sure …
>
> The combination of the constellation and the ionosphere are what I believe
> give you the once a day (rather than once per 12 hours) bump.
>
> Bob
>
> > On Oct 20, 2014, at 3:43 AM, Magnus Danielson <
> magnus at rubidium.dyndns.org> wrote:
> >
> > Bob,
> >
> > Since the satellite orbit the earth with a period of 11 hours and 58
> minutes, it is actually twice a day.
> >
> > Cheers,
> > Magnus
> >
> > On 10/20/2014 03:50 AM, Bob Camp wrote:
> >> Hi
> >>
> >> 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.
> >>
> >> Bob
> >>
> >>> 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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