[time-nuts] GPS jump

Neil Schroeder gigneil at gmail.com
Sat Oct 11 00:55:25 EDT 2014


No. They don't directly if that's what you mean.  They do regular time
transfers, likely more regularly than most due to accessibility to a common
view and common interest.

The GPS consolation is actually a sub-(sub?)-scale of UTC(USNO_MC) called i
think USNO_OSC?  Have to check.

They have been building out the  timescale ensemble at Schriever
significantly over yhe last 5 or so years. They were up to 26 references
planned last  i spoke with anyone back home - the delta being primarily
H-masers.

I think that's a good move. Despite Timefreq being just  about  2 hours
away, that master clock's survivability  was never certain.  Shipping the
timescale to Colorado Springs from Wisconsin Ave/Bethesda did contain risk,
and they are mitigating it.

I was once told - total anecdote and certainly 15 years ago - that despite
proximity and willingness they rarely exchange views or collaborate
experimentally between Colorado Springs and Boulder. Silly in  my mind but
it is an a active weapons platform and the logistics may not be conducive.

NS



On Friday, October 10, 2014, Brian Inglis <Brian.Inglis at systematicsw.ab.ca>
wrote:

> On Oct 9, 2014, at 7:43 PM, Jim Palfreyman <jim77742 at gmail.com> wrote:
>>>
>>
>  We look after 5 separate hydrogen masers spread all over Australia and we
>>>> collect tic phases between the masers and the GPS.
>>>>
>>>> On around ~Oct 7 we have noticed that the normal steady straight line
>>>> (with
>>>> standard daily noise) took a noticeable downward turn - on all 5 masers.
>>>>
>>>
>  On 2013-10-03 05:33, Jim Palfreyman wrote:
>>>>
>>>
>  Noticed an above average bump in our H-Maser vs GPS graphs - from sites
>>>>> all over Australia.
>>>>>
>>>>> Recent coronal mass ejection or US government shutdown not updating
>>>>> GPS?
>>>>> Anyone else seen it?
>>>>>
>>>>
>  drop out gap between about 04.21-04.26 UTC?
>>>> clockstats.20131003:
>>>> 56568 15684.876 127.127.20.4 $GPRMC 042124 A ...
>>>> 56568 16004.862 127.127.20.4 $GPRMC 042644 A ...
>>>> peerstats.20131003:
>>>> 56568 15684.876 127.127.20.4 961a -0.000002270 ... 0.000005344
>>>> 56568 16004.862 127.127.20.4 961a -0.000013150 ... 0.000015721
>>>> loopstats.20131003:
>>>> 56568 15684.876 -0.000002270 0.899 0.000007071 0.000070 4
>>>> 56568 16004.862 -0.000013150 0.898 0.000008830 0.000114 4
>>>>
>>>
>
>>>> Did anyone else who tracks H-masers notice this as well?
>>>>
>>>> Is it JPL making corrections?
>>>>
>>>
>  Le 10 oct. 2014 à 03:09, Bob Camp a écrit :
>>
>
>  GPS is steered by the Air Force last time I checked.
>>> A really good place to check is the NIST Time and Frequency pages that
>>> show both real time and historical data for each GPS sat compared to NIST
>>> time:
>>> http://www.nist.gov/pml/div688/grp40/gpsarchive.cfm
>>> Hopefully it’s accessible via that link from a variety of locations.
>>> Since the NIST data is independent of the steering (two different
>>> outfits involved) it should not be vulnerable to a “our ground segment
>>> broke and we steered everything to match” sort of error.
>>>
>>
> On 2014-10-09 23:06, mike cook wrote:
>
>>    I remember Jim reported a similar issue back in october last year:
>>
>
>     That dates are close enough to make you wonder if it is not part of
>> some cycle.
>>
>
> From: http://www.usno.navy.mil/USNO/time/gps/gps-info
> GPS SYSTEM TIME
> GPS system time is given by its Composite Clock (CC).
> The CC or "paper" clock consists of all operational Monitor Station and
> satellite
> frequency standards. GPS system time, in turn, is referenced to the Master
> Clock
> (MC) at the USNO and steered to UTC(USNO) from which system time will not
> deviate
> by more than one microsecond. The exact difference is contained in the
> navigation
> message in the form of two constants, A0 and A1, giving the time
> difference and
> rate of system time against UTC(USNO,MC).
>
> Page also gives links to GPS time data ftp://tycho.usno.navy.mil/pub/
> gps/utcgps30.dat
> which shows a 2ns jump in UTC(USNO)-GPS smoothed over 2 days from Oct 7-8,
> but that
> appears normal; the <1ns differences from Oct 2-7 appear anomalous.
>
> Looking at the NIST 10 min data, from Oct 3-8 the gap between GPS samples
> and NIST
> closed about 1.5ns/day, dropping now to about .5ns/day: the graph shows
> the values
> sliding down to the right, and now levelling off about zero.
>
> So are NIST and USNO steering each other?
>
> --
> Take care. Thanks, Brian Inglis
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