[time-nuts] "GPS once a day issues" ?
kb8tq at n1k.org
Mon Oct 20 07:15:40 EDT 2014
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.
> On Oct 20, 2014, at 3:43 AM, Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day.
> On 10/20/2014 03:50 AM, Bob Camp wrote:
>> 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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