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

Paul Boven p.boven at xs4all.nl
Thu Jan 28 01:58:05 EST 2016


Hi Martin,

On 2016-01-27 17:49:52, Martin Burnicki wrote:
>>> 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).
>>>
>>> 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.

Thanks for posting this, it's great that you managed to actually record 
those frames. This explanation fits the observed behaviour (steps of 
around 13us all over the world) much better than a malfunction of SVN 
23. Furthermore, SVN 23 had already been decommissioned prior to these 
events.

Regards, Paul Boven.




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