[time-nuts] time-nuts, frequency counters

David Forbes dforbes at dakotacom.net
Wed Sep 26 17:55:58 EDT 2007

CHazlitt wrote:
> So, here is my question, do Rubidium standards drift that much over a period 
> of years to where they have to be brought back on frequency? If so, what is 
> tuned on the Rubidium to do so, C-field? 

Yes, they do drift over time. There is a spec provided on the data 
sheet; you can expect the unit to drift at perhaps half of that 
specified maximum rate. You can adjust the magnetic field to bring it 
back to center frequency, but sometimes they drift so much (over >10 
years) that you have to replace a factory-selected resistor to get the 
trimmer into range.

The only type of commercially available frequency standard that doesn't 
drift is a cesium beam clock; their frequency of operation doesn't 
depend on magnetic fields or buffer gas pressure or anything like that. 
That's why they're used for GPS etc.

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