[time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Bob Camp]

HI

If you have a good antenna location and always have more sat’s in view than the receiver can use, 
the constellation shift may not be a big deal at some level. No matter how good the antenna, day / night
ionosphere compared to the estimated numbers they broadcast will be an issue. 

Is the level that the local multi path and the constellation "gets you" higher than the level that the ionosphere 
correction falls apart? Without a lot of data, you will have a hard time sorting that out. 

All of that said, I have seen “glitches” in long term plots that space out at the expected “just short of 24 hours” 
period. In my location and with the gear I’m running … it’s more likely the constellation than the ionosphere. 
The glitches are to narrow (short duration) and far to regular for the ionosphere to be the issue. 

Bob



> On May 23, 2016, at 11:52 PM, Skip Withrow <skip.withrow at gmail.com> wrote:
> 
> Hello Bob,
> 
> Good point.  Ionosphere between day and night could very well explain it.
> 
> Thanks,
> Skip Withrow
> 
> On Mon, May 23, 2016 at 5:37 PM, Bob Camp <kb8tq at n1k.org> wrote:
> Hi
> 
> Well, *maybe* there is a 24 hour component in the GPS constellation :)
> 
> Indeed a lot of stuff repeats at the 24 hour point. The ionosphere is a bit different at midnight than at noon.
> 
> Bob
> 
> > On May 23, 2016, at 6:43 PM, Skip Withrow <skip.withrow at gmail.com> wrote:
> >
> > Hello Nuts,
> >
> > I am attaching a capture from Lady Heather of a 3-day run.  You can see the
> > temperature vary by 7C over each day.  The TB is being run open loop and
> > another GPSDO 10MHz input to the unit instead of the unit's oscillator.
> >
> > I expected the purple line to repeat every 12 hours based on the GPS
> > constellation being the same (which maybe it kind of does), but there is
> > definitely a 24 hour repeat.  What is really weird is that the number of
> > satellites that LH sees also repeats on a 24 hour cycle, not 12 (bottom
> > trace).
> >
> > Any help in understanding this behavior?  Thanks in advance.
> >
> > Skip Withrow
> >
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