[time-nuts] GPS jumps of -13.7 us?

Magnus Danielson magnus at rubidium.dyndns.org
Wed Jan 27 00:15:53 UTC 2016


On 01/26/2016 11:46 PM, Martin Burnicki wrote:
> Paul Boven wrote:
>> Hi everyone,
>> Has anyone else seen GPS time jump by -13.7 usec today?
>> I just heard from several geographically quite distributed radio
>> observatories that they have seen their GPS receiver(s) jump compared to
>> their in-house standards.
> We were able to track this down today at Meinberg.
> The problem was that some satellites were sending invalid UTC correction
> parameters. The UTC correction parameter set not only contains current
> leap second information but also coefficients (A0, A1, WNt, tot) for a
> polynomial used to compensate the fractional difference between GPS time
> and UTC(USNO).
> Normally A0 (the constant offset) is very small, close to 0. WNt and tot
> give the week number (truncated to 8 bits) and second-of-week for which
> A0 is valid, i.e. the reference time for the time correction parameters.
> WNt is currently about 89.
> Today the faulty satellites sent about 13.7 microseconds for A0, and WNt
> as well as tot were both 0. So when the GPS receiver updated its UTC
> correction parameters from a faulty satellite the UTC correction jumped
> from close to 0 to about 13.7 microseconds, which let the UTC time step,
> and when the GPS receiver received the UTC parameter set from a healthy
> satellite the UTC time stepped back.
> We have recorded a few of the faulty subframe words. If someone is
> interested I can provide more detailed information. However, I'm
> currently out of the office and don't have the information here right now.

You know I want more details. ;-)

I did see the report you guys sent to the USCG, good work there and good 

I also some another report showing issues with other SVNs.


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