[time-nuts] Ublox 6T receiver, noisy PPS.

dan at irtelemetrics.com dan at irtelemetrics.com
Fri Jan 16 19:03:44 EST 2015

     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 
  I'm quite puzzled by this sudden degradation of the system. 

More information about the time-nuts mailing list