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

[Michael Wouters]

Dear Sean,

The USNO is the main source of precise time in the US via the GPS system.
It has an ensemble of caesium clocks and hydrogen masers in Washington that
it uses as the reference to provide corrections for the clocks that are
onboard each of the GPS satellites. These corrections are broadcast
continuously via the GPS system.

What your boss is referring to is Coordinated Universal Time (UTC), the
international time standard. National labs which operate atomic clocks
compare their clocks using a variety of methods and send these to the BIPM,
which makes a weighted average of the all of the participating clocks (for
stability) and combines the ten or so primary frequency standard
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.

You can find the monthly reports in Circular T.

NIST also maintains an ensemble of atomic clocks and contributes to UTC.
However, in addition to commercial caesium beam standards and hydrogen
masers, they have several primary frequency standards, in particular,
caesium fountains.


Regards
Michael

On Wednesday, 13 April 2016, Sean Gallagher <sean at wetstonetech.com> wrote:

> I recently wrote a paper for school on precision time and from my research
> it seems that the US Naval Observatory is the main source of time for the
> United States. So I would assume that this is also true for the Master
> Control Station in Colorado and that they get their source time from the
> Observatory as well? I emailed the GPS.gov site and got an answer that they
> do indeed have clocks there but he was unsure of their source time because
> he was the webmaster for the site and so is not intricately tied in to the
> system.
>
> What's throwing me off though is that my former boss wrote up something
> for work where he states that the satellites get their time from BIPM? He
> is older and wiser than I am but I think that at this point I have probably
> done more research on it all so that's why I am not accepting his word
> immediately but also not writing it off.
>
> NIST is another option but it appears as if they are more about research
> correct?
>
> Respectfully,
>
> Sean Gallagher
> Malware Analyst
> 571-340-3475
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