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

Azelio Boriani azelio.boriani at gmail.com
Fri Jan 16 20:28:47 EST 2015

I have noticed the sudden improvement of the PPS wander after the
survey on a LEA-5T but the RMS wander is 30ns (see the timing appnote
GPS.G6-X-11007 from uBlox) uncorrected and 15ns if sawtooth corrected.
Your 3ns is strange, not the 30ns.

On Sat, Jan 17, 2015 at 1:03 AM,  <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.
>  Thanks,
>  Dan
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