[time-nuts] Exact Rubidium frequency

[Peter Vince]

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)