[time-nuts] Exact Rubidium frequency
brooke at pacific.net
Sat Jun 30 21:39:43 EDT 2007
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
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
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
> 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
> (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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