[time-nuts] Rubidium Drift

John Ackermann N8UR jra at febo.com
Fri Nov 3 09:04:34 EST 2006

Tom Van Baak wrote:
>> I've recently acquired a Rubidium Osc ( Efratom FRS-C 10Mhz) as my 
>> first venture into this field. It's working as per the spec given 
>> ,checked against Trimble GPS with 1pps output.
>> Can you point me to somewhere where there is  a description of the 
>> physics behind the drift that occurs?Drift is speced as <5x10^-11 per 
>> month....but why should there be any "drift" at all?
>> "Wandering" about nominal I can expect ,but consistent "drift" ?
>> Regards
>> Peter
> Hi Peter,
> You're off to a good start. With enough days of data
> you should be able to measure the drift quite nicely.
> To answer your good question; we all have come to
> know that cesium is accurate and rubidium drifts. But
> there's much more to the story...

[ Tom's good stuff snipped ]

For what it's worth, I have plots with (at the moment) 98 days worth of 
data showing two HP 5061As and an HP 5065A against GPS (and each other) 
at http://www.febo.com/time-freq/plots.  The drift of the 5065A is hard 
to discern because what I presume are other environmental effects hide 
it; in other words, it's pretty darn low.

You'll see a whole bunch of files there with hopefully reasonably 
explanatory names like "cs1-gps-hourly.html" which shows CS1 vs. GPS 
with hourly averages.  The files with "-daily" are 1 day averages, while 
the ones with "-tail" show the seven most recent days of data with 10 
minute averages.

Each web page shows the raw phase, the drift-removed phase (using a 
linear calculation of drift) and ADEV as well as some other statistics. 
  The pages are automagically updated every 15 minutes.

I'm hoping to keep the experiment going for a while longer; I'd like to 
get out to at least 120 days of data.  I can make the raw data available 
if anyone is interested.


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