[time-nuts] time-nuts, frequency counters
smace at intt.net
Wed Sep 26 18:24:42 EDT 2007
I picked up one of the Lucent RFG-RB units on ebay and sure enough it was
off, but not by much. It was manufactured mid 2001. I adjusted the
C-field pot while comparing it to my best z3801a. I'm waiting on a
new GPIB interface to see just how well I did. The LPRO-101 in the
RFG-RB makes about 15W of heat. I gently clamped it to the back heatsink
of the RFG unit and left it on for an hour or two before adjusting with
my counter in TI mode. I thought about drilling a small hole in the top
of the RFG chassis so I could access the C-field pot, but decided I just
liked taking the thing apart...
David Forbes wrote:
> 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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