[time-nuts] Comparing Reference Accuracy

[Angus]

On Fri, 23 May 2008 09:26:43 +1200, you wrote:

>The errors of the various GPSDOs cannot be determined without access to 
>a primary standard.

Has anyone here tried to squeeze extra medium term performance out of
a rubidium by controlling (or compensating for) environmental factors
like temperature and pressure?  Not having a decent reference for
testing GPSDOs was one thing that made me want to see what could be
done, although I'd been wanting to try it for a long time anyway. 

I recently got around to testing an LPRO against GPS, and the
stability was still a fairly useful 1E-13 at 1 day. It was in a
temperature controlled housing, and had an analogue pressure sensor
connected up to it to adjust the c-field to compensate for air
pressure changes - not a perfect setup, but as an experiment it was
definitely promising.

I'm not suggesting that it would be as good as a primary standard, but
it could be useful in some circumstances, either stand-alone or
steered to GPS.

The only paper I came accross which deals specifically with this is a
rather short one where FE5650A's were tested: "The Effects of Ambient
Temperature Fluctuations on the Long-Term Frequency Stability of a
Miniature Rubidium Atomic Frequency Standard" 

Angus.