[time-nuts] TBolt: UTC PPS

[Magnus Danielson]

Tom Van Baak wrote:
>> It also has an option to sync the PPS with GPS or UTC.  I thought 
>> they were off by an integral number of seconds so I don't expect any 
>> change.  Does anybody know what's going on here?
>
> The GPS broadcast message includes leap second and
> a0 and a1 terms which are used to forward predict UTC
> from GPS time, which is derived from UTC(USNO).
>
> A0 and A1 are what you'd guess: a phase offset and a
> frequency offset.
>
> See page 157 of the GPS ICD:
> <http://www.navcen.uscg.gov/gps/geninfo/ICD-GPS-200C%20with%20IRNs%2012345.pdf> 
>
>
> So yes, at the ns level the two 1PPS will differ since UTC
> is not the same as UTC(USNO) or any other UTC(k) for
> that matter. Have you measured it? I would be interested
> to know what the delta is for your receiver today. You
> can also dump out the a1 and a0 corrections with binary
> commands on some GPS receivers. 
The GPS time is steered towards UTC(USNO) to be maintained within 1 us. 
The effective difference is in a few ns. I could dig up the webpage at 
USNO giving the difference if needed to. (TvB already has a mail from me 
on this topic)

There should be no effective difference between them.

Cheers,
Magnus