[time-nuts] Re: Long term ADEV of 5071

[Demetrios Matsakis]

The BIPM’s new algorithm, implemented around 2014, weights clock by their predictability, and also estimates the frequency drift of the masers.  That’s why masers have risen to their level of prominence.  But masers do have all kinds of variations at some level, which I easily saw when I worked at the USNO and had decades of data uncorrupted by time transfer noise.  I was going to publish a paper in 2019, but I didn’t because getting approval was impossible.  It will be interesting to see what you guys can come up with using BIPM data to create long time series of frequency variations for cesiums and masers too.   Be careful because the BIPM data may not tell you when a cesium beam tube was changed, or a maser underwent repair.  Or a clock was moved.   So I would treat any data gap as a new clock.

Maybe one year ago Microsemi started advertising lower drift in their masers, and I suspect that is because they found a way to compensate for the initial drift so the user doesn’t see it.  (I have no idea if this is really true.)  Years ago in a paper I published with Mike Garvey and Paul Koppang I found the frequency drift noticeably decreased after three years.   Extending my unsupported theory, that might mean new masers pick up a drift over time.   But components change, and whatever they do can be modeled.

Another thing about the meaning of weights is that clocks used to be characterized through comparison with the EAL timescale, which does not involve primaries.   But the new algorithm characterizes them against a TT-guess which carries the frequency of the primaries.  So that in effect degrades masers, cesiums, and Rb fountains to the status of frequency interpolators between the primary standards.   (This is an observation I have made many times and no one has contradicted me, so I guess it is obvious.)

> On Mar 28, 2021, at 12:28 PM, Tom Van Baak <tvb at leapsecond.com> wrote:
> 
> The pie charts that Anders created show clocks in the UTC "flywheel". That excludes most research fountains and optical clocks because they can't or aren't run continuously.
> 
> Of the 427 clocks [1] in that data set there are 247 5071A (58%) and 167 H-masers (39%) and 6 fountains (<1.4%). So the short answer to your question is that there are only 6 fountains in the chart: 4 Rb fountains at USNO and 2 Cs fountains at PTB.
> 
> When playing with charts, it's important not to confuse the number of clocks with the weighting of clocks. And even the weighting is misleading because for practical reasons any clock's weight in UTC is capped at about 1%. All 4 of USNO's Rb fountains are at this level, for example. About 60 of the H-masers are also at this level. And none of the 5071A; not even close.
> 
> If you are a 5071A sales person you are likely to emphasize that 60% of the clocks in UTC are 5071A. You are less likely to mention they contribute only 8% of the weight these days.
> 
> If you are in H-maser sales you can claim 40% of the clocks in UTC are masers and also they contribute 88% of the weight.
> 
> It's a good time to be in Microchip clock sales: they now own both the hp 5071A and the Sigma Tau H-maser manufacturing plants. Yes, they still make PIC chips too ;-)
> 
> /tvb
> 
> [1] https://webtai.bipm.org/database/clock.html
> 
> - clock type 35/36 are 5071A
> - clock type 40/41 are H-masers
> - clock type 92/93 are Cs/Rb fountain
> 
> 
> On 3/28/2021 6:15 AM, Bob kb8tq wrote:
>> Hi
>> 
>> I would *guess* that fountains would be in there somewhere ( at least in the
>> 2021 version ).
>> 
>> Bob
>> 
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