[time-nuts] Cs stability
magnus at rubidium.dyndns.org
Tue Jul 17 13:28:31 EDT 2007
From: "Richard \(Rick\) Karlquist" <richard at karlquist.com>
Subject: Re: [time-nuts] Cs stability
Date: Tue, 17 Jul 2007 09:52:22 -0700
Message-ID: <MGEKKFGEAIKJOOPJPGIKAEGFJEAA.richard at karlquist.com>
> In case anyone still doesn't know who I am, I need to
> mention that I designed the RF electronics in the
> 5071A in an earlier life, circa 1990.
> Now that we have that out of the way, I will agree
> with Magnus that the cited paper is severely flawed.
Good, then I am not the only one seeing that. I must admitt that I didn't give
it a comprehensive readthrough asI was tired as hell when I looked at it, but
I did not get the necessary ques as I browsed through it and even as I dipped
into certain parts in detail it left me unsatisfied.
> We don't know what models of cesium were used, and
> the paper seems to assume that any deviations with
> respect to GPS are due solely to the cesium standards.
> We also don't know anything about the GPS equipment.
> Citation  is a 5071A product note. I guess this
> is thrown in to imply that one of the cesiums is a
> 5071A; but we can't be sure.
There is only an indirect reference to 5071A in a.
> A statement is taken
> out of context from this product note to the effect
> that "some cesiums don't have an independent means
> of frequency setting", which might lead the casual
> observer to think that this refers to the 5071A.
> Actually, the 5071A does have an independent means
> of frequency setting, as opposed to older cesium
> clocks where you had to vary the C-field to change
> the frequency. For this and other reasons, I don't
> put much stock in the paper.
Do note that he in the introductionary part shows the factor deviation of
2.7E-13 and that he adjusted it manually twice which can be seen in the second
"Unfortunately, many atomic oscillators lack the possibility of non-invasive
frequency tuning . Using digital correction, the frequency offset of
2.7 E-13 as delivered from factory is shown in Fig.l to be reducable below
1 E-14 with only two frequency corrections at 1800 and 4O00 hours from
start-up, leaving some environmental factors plus a number of unpredictable
timing discrepancies lasting 50-500 horn."
He actually points out that the 5071A lacks that correction, so he agrees with
you. This correction can be done by him as an initial post-processing step.
We just don't know, again. A little sentense or two more on how that was made
would have enlighen us further on that subject.
But what Cesium he actually used is not known.
> I hope this clears up any confusion about the 5071A, now
> made by my good friends at Symmetricom.
Many, many thanks for the write-up. I greatly enjoyed it!
More information about the time-nuts