[time-nuts] Ublox 6T receiver, noisy PPS.
John C. Westmoreland, P.E.
john at westmorelandengineering.com
Fri Jan 16 20:36:38 EST 2015
I have a LEA-6T running; have a nice external antenna, etc - it's been
running for several days - I will check the 1PPS and report if I find
anything like what you've discussed.
On Fri, Jan 16, 2015 at 4:03 PM, <dan at irtelemetrics.com> wrote:
> Hi All,
> I've been playing a Ublox 6T receivers on a synergy SSR-6Tru module. The
> unit has been running as part of a GPSDO. In logging the phase between GPS
> PPS and OXCO, a few days ago the normally small amplitude short term (10s
> to ~500s) phase wander became rather erratic. For the previous several
> months the short term wander was around +/- 3nS to 5nS. All of a sudden
> this jumped up to about +/- 25nS.
> Anyway, the guess was that it was GPS related. So the first step was to
> verify GPS was still using the last survey-in points, which it was. The
> modules was seeing 14 or 15 good birds at a signal strength of 35 to 50.
> For kicks another survey in (48 hour) was started, which just finished up
> today. As soon as the survey in completed the phase wander dropped back
> down to about +/-3nS. The change was immediate, like a switch was thrown.
> The antenna hasn't moved, but the corresponding survey coordinates from
> September and January show a phase center position change of about 1.8m.
> This seems like a pretty small number, and wouldn't have expected it to
> make that big of a difference. At this point I'm not sure what to think.
> Has anyone seen any of the Ulbox 6T modules PPS suddenly get 'noisy'. Is
> there anything else I should be looking at?
> Any recommendations on what I should be setting for NAV5 and NAVX5
> settings that could improve things? Elevation angles, or C/N thresholds?
> I'm quite puzzled by this sudden degradation of the system.
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