[time-nuts] Where does the source time for GPS come from?

[Attila Kinali]

On Wed, 13 Apr 2016 08:50:13 -0700
"Richard (Rick) Karlquist" <richard at karlquist.com> wrote:

> Also note that there is a division of labor between
> cesium clocks, which run continuously to keep time,
> but may not be as accurate as "big" cesium standards
> in terms of frequency.  However, the big standards
> may not run 24/7 so they function as frequency standards
> as opposed to true clocks.

At our visit at METAS i was told, that the Cs foutain is powerd
up once a week to measure the exact frequency of the H-Maser
and the three 5071's they have.


> There is also the whole issue of "time transfer" among
> all these devices.  The gold standard is 2 way satellite.
> But the everyday method is GPS itself.

The gold standard is actually fibre. With that it's possible
to do sub-ns time transfer and <10^-16 frequency transfer (in a day).
But the longest fibre links are limited to a couple of 1000km. 
Currently, there is a fibre link between Syrte (Paris) and PTB (Braunschweig)
over Strassbourg. It is planned to extend that to NPL (Middlesex)
and to INRIM (Turin). There is also a fibre from PTB to MPI-QP (Munich)
and it's likely that this will be integrated into the above network as well.
In east europe, there are also few fibre links, but these are considerably
shorter and have no interlinks yet (and no planned, as far as i am aware of).

			Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson