[time-nuts] Frequency Ensemble

[Attila Kinali]

On Sun, 17 Mar 2019 12:00:11 -0700
"Tom Van Baak" <tvb at LeapSecond.com> wrote:

> So yes, NIST, USNO, PTB, BIPM -- all the big boys -- use ensemble 
> techniques. But the key is that they mostly use cesium clocks, not OCXO or 
> Rb clocks from eBay. Laboratory cesium standards don't suffer from frequency 
> drift. The other key is that the clocks are independent. Under these 
> conditions one can obtain sqrt(N) advantage.

Most of the Cs beam standards contributing to TAI are 5071s.
And, unfortunately, they do drift. As do almost all of the
atomic clocks contributing to TAI. There are a handful of
labs (IIRC 8) that run "the primary standards" which have
a low enough uncertainty of influences to be considered
non-drifting. IIRC all of them are are Cs fountains.
Also unfortunately, most of these cannot or are not operated
continuously. But according to METAS they don't need to be
as the 5071s are stable enough that measuring their frequency
once a month is enough to keep the uncertainty below what
time and frequncy transfer can deliver today.


			Attila Kinali

-- 
<JaberWorky>	The bad part of Zurich is where the degenerates
                throw DARK chocolate at you.