[time-nuts] time-nuts, frequency counters

Rick Karlquist richard at karlquist.com
Wed Sep 26 18:19:29 EDT 2007


Rb's drift typically 10^-10 to 10^-11 per month,
about 100X better than the best quartz.  We hit the
latter number on the pilot run of the HP10816 Rb.
There are many drift mechanisms, which can be related to physics,
chemistry, optics, magnetics, or electronics.  If
an Rb apparently has no drift, it really means the
drift mechanisms are temporarily cancelling.  They
won't do this over the long run.

Newer Rb units may use adjustment of the internal synthesizer
in place of modifying the C-field.  There are many disadvantages
to modifying the C-field.

Rick Karlquist N6RK

David Forbes wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+richard=karlquist.com at febo.com RETRY
>
> 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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