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

[David Forbes]

At 2:33 PM +0100 11/6/06, Ulrich Bangert wrote:
>Hi Poul-Henning,
>
>>  They don't have a "correct" frequency, only a very stable frequency.
>>
>>  The actual resonance frequency of a rubidium standard depends
>>  amongst other things on the partial pressures inside the
>>  physics package.
>
>We are well aware of these facts! But if THAT were the reason to correct
>for with different thumbwheel settings would not EVERY rubidium standard
>in the world desperately need this kind of correction feature?
>
>Both my FRK-L and my LPRO need only C-field correction to get the
>nominal 10.0000000 MHz out of it. Or has HP not been able to build the
>physics packages more 'repeatable'?
>
>Cheers
>Ulrich

Ulrich,

We have a 13 year old rubidium standard at my place of work that 
drifted by about 1.5E-9 over its lifetime. This is within factory 
specifications, but beyond the range of the C-field adjustment 
trimpot.

The rubidium vapor method does not generate anything like an exact 
frequency; it can vary quite a bit depending on the lamp, the gas, 
etc. The unit I was testing has a fixed resistor that is factory 
selected to set the C-field control in the middle of its range when 
the device is new. I could bring the C-field control back into range 
by changing that resistor if desired. That's apparently standard 
procedure for these devices.

-- 

--David Forbes, Tucson, AZ
http://www.cathodecorner.com/