[time-nuts] Frequency processing scheme of HP5065 vapourrubidium standard

Rob Kimberley time.bandit at btinternet.com
Tue Nov 7 12:06:01 EST 2006


What about the Rubidium Fountain?

See first article in the Autumn 2005 report at link below.

http://www.npl.co.uk/publications/news/time/

Rob Kimberley
 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Normand Martel
Sent: 07 November 2006 00:29
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Frequency processing scheme of HP5065
vapourrubidium standard



--- Ulrich Bangert <df6jb at ulrich-bangert.de> wrote:

> John,
> 
> > offset that changed annually.  IIRC, it was
> typically something like
> > 300x10e-10.
> 
> Agreed! And that is what the manual says its good for!
> 
> However, the question remains why different physics packages need 
> DIFFERENT thumbwheel settings in order to achieve the SAME time scale.
> 
> 73 de Ulrich, DF6JB
> 
I've read the answer last week on the forum... (sorry i don't remember who
gave the answer...)

It's simple: The technology used on cesiums CAN NOT be applioed on
Rubidiums. With Cesium, high end techniologies like fountains or beans can
be used, and if i understand well, with these technologies, PURE CESIUM is
used, so there is NOTHING that can affect or "pull" the resonance of cesium
from it's natural resonance. (9 192 631 770 Hz).

With rubidium, buffer gases must be used, and these gasses "pull away" the
resonance away from Rubidium's natural resonance. And that is the source of
all our problems with rubidium: Buffer gas/rubidium evaporation/absorption
will affect the frequency "pulling", thus the drift in Rubidiums. This also
explins why two rubidiums clocks wiill have different settings (Rb/buffer
mixture tolerances). With Cesium, no pulling, with rubidium, some pulling.
That's why Rubidiums aren't primary standards. If we could build a Rb (or
ANY OTHER element) atomic clock with the same technology that we use with Cs
(total element purity), there wouldn't be any pulling over time and Rb's
would be considered primary standards.

Hope this explanation will help!

73 de Normand Martel VE2UM






 
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