[time-nuts] How Rubidiums make their frequency (was RE:time-nuts Digest, Vol 21, Issue 22)

Robert Lutwak Lutwak at Alum.mit.edu
Thu Apr 20 06:03:39 EDT 2006

Most rubidiums have two tuning adjustments, one for the cavity frequency and 
one for the lamp RF frequency.  I'd start by tuning those properly and see 
how your frequency offset changes.

Somewhere on the servo you'll find a test point for observing the second 
harmonic of the modulation.  Clip that to your oscilloscope and adjust the 
cavity tuning for maximum response.

Somewhere else, you should find a DC light level monitor, tune up the lamp 
frequency for maximum light.

One or the other (or both) of these adjustments may move the frequency back 
towards the midpoint of the C-field adjustment.  If you get them optimized 
it'll also improve the temperature sensitivity and long-term drift.


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----- Original Message ----- 
From: "Christopher Hoover" <ch at murgatroid.com>
To: <time-nuts at febo.com>; <K3IO at verizon.net>
Sent: Thursday, April 20, 2006 5:31 AM
Subject: Re: [time-nuts] How Rubidiums make their frequency (was 
RE:time-nuts Digest, Vol 21, Issue 22)

> Tom Clark wrote:
>>   Christopher Hoover asked:
>>> one issue remains:   i have to crank the magnetic field setting almost 
>>> to
>>> its high limit (9.91/10.00) to get 5 MHz out; lower settings give a
>>> frequency that is too low.   i presume this is unusual.
>>> i have a rudimentary understanding of the rubidium oscillator physics,
>>> but i do not understand what would cause this.  can i buy a clue?
>>   I don't know the Tracor, but I imagine it is like most of the other
>>   Rubidiums in it's innards.
> Hi Tom,
> That's a good explanation, thank you.   I got that much already.  (While 
> it
> took some time for my phyiscs, chemistry and semiconductor physics studies
> to kick back in, it all clicked last week.)   The Tracor, indeed, seems
> fairly ordinary compared to the other Rb's I have, going by the test 
> points
> and the various labels inside.   There is the typical synthesizer section,
> audio demodulation section for the photocell, etc.
> So what I'm really wondering is this: is there a  wear mechanism or 
> failure
> mode in the physics package that might explain why I have to crank the mag
> field almost to its high limit to get 5 MHz?  (This question presumes the
> mag field control is working properly, and I cannot say for sure that it
> is.)
> Thanks,
> -- Christopher.
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