[time-nuts] Exact Rubidium frequency

Brooke Clarke brooke at pacific.net
Sat Jun 30 21:39:43 EDT 2007

Hi Peter:

Yes, as far as I can tell all oscillators have an adjustment to allow changing 
their frequency, including the C Filed adjustment on a Cesium standard.  The 
key difference is that with the Cesium standard, by definition, it does not 
drift.  So if you make a phase plot comparing any oscillator to say a timing 
grade GPS receiver the shape will be parabolic or some higher polynomial.  But 
for a Cesium it will be a straight line.

The more modern Cesium standards have control loops that automatically set the 
C Field and maintain it so do come very close to the plug and play idea.  But 
the first few generations of Cesium standards need to be tweaked on frequency.
The HP 5060 C Field adjustment is so coarse that a modern Rubidium standard is 
more accurate.

http://www.prc68.com/I/5060A.html <- C Field step size near 1E-10 if you use 
the smallest mark on the vernier of the 10 turn pot

http://www.prc68.com/I/FTS4060.shtml <- C field step size near 1E-14, 3 digit 
thumb wheel.

Have Fun,

Brooke Clarke

Peter Vince wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+brooke=pacific.net+brooke=pacific.net at febo.com
> Everyone on the 'net agrees on the frequency of the Caesium 
> oscillation, but the precise frequency quoted for Rubidium varies by 
> a few Hz :-(  Now I realise that you can make it anything you like 
> (within reason) by altering the magnetic field, and perhaps different 
> sources quote different figures which are more or less easy to 
> synthesise?
> On the (USA) NIST web-page 
> (http://tf.nist.gov/general/enc-re.htm#rubidiumoscillator) they quote 
> 6,834,682,608 Hz, but the (German) PTB (on 
> http://www.ptb.de/en/org/4/44/441/info2_e.htm) give 6,384,682,612.8 
> Hz, and the (British) NPL quotes 6,834,682,610.904 324 Hz in a 
> powerpoint presentation 
> http://www.npl.co.uk/time/club/meeting1/secondaryrepsec.pdf 
> (admittedly for a Rubidium fountain).
> I have also seen the frequency of a Hydrogen Maser given as both 
> 1,420,405,751 Hz and ...752 Hz.  I would be very surprised if the 
> frequency was an exact whole number of Hertz different from Caesium, 
> so perhaps this is just rounded for convenience as again it can be 
> steered to anywhere you like?
> Would anyone care to comment on this differences please?
> 	Thank you,
> 		Peter Vince  (G8ZZR, London)
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