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

Richard (Rick) Karlquist richard at karlquist.com
Wed Apr 13 15:50:13 UTC 2016



On 4/12/2016 3:16 PM, Michael Wouters wrote:
>
> evaluations (for accuracy) to finally get its best estimate of what one
> second is. Each participating lab is then told what the difference between
> its clock and UTC is.
>
> USNO participates in UTC and keeps within tens of ns of UTC.

It might also be useful to introduce the concept of a "paper
clock", as opposed to a physical clock.  A paper clock
is where a lab has a physical clock that is compared to
UTC and they get an after the fact report that gives
them a correction factor to apply to their clock.  This
makes a paper clock.  So they can't tell you what time it
is now to a high degree of accuracy, but they can tell
you exactly what time it was last week.

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.

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.

Rick



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