[time-nuts] Ublox 6T receiver, noisy PPS.
kb8tq at n1k.org
Fri Jan 16 19:58:01 EST 2015
It sounds like you are not doing sawtooth correction. If that is correct, then you may have been watching hanging bridges.
> On Jan 16, 2015, at 7:03 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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