One method of reducing the sensitivity to magnetic fields is to enclose
the rubidium source in a series of nested magnetic shields (e.g. mu metal).
The shield walls could form part of the good thermal conductor poor
thermal conductor stack.
One could also use something like a set of 3 orthogonal Helmholtz coils
to null the magnetic field at the rubidium source.
A servo loop using a magnetic field sensor could be employed.
Bruce
Bob Camp wrote:
Hi
To tune the frequency of a rubidium, you make a very small change to the DC
magnetic field around the cell. That's the way you put them on frequency.
Anything that changes the local field also changes the frequency of the
rubidium standard.
The DC in the power leads is a constant current and therefore creates a
non-changing field. That means no frequency change.
The reason you change the current in the heater is to stabilize the rubidium.
If while you are trying to stabilize it one way, you de-stabalize it another
way, that may not be progress.
I believe that putting a couple of watts of RF into the heater is not a very
practical thing ....
Bob
On Dec 24, 2009, at 2:14 PM, WarrenS wrote:
I Must not get it, Or I'm missing something.
Some seem to be going on and on about a little added DC heater current that can
be held to about 10% of what the unit draws
Why does a little added DC heater current any more of a problem that what you
do with the leads etc of the main power?
(And with a few simple tricks you can also reduce the effect of the changing
heater current so it has insignificant effect)
Have to work a bit harder to say the same about putting AC or RF into the heater
ws
***************
Bob Camp wrote:
Hi
Having a bunch of AC current gets me into another issue. I suspect it's going
to couple into something somewhere and give me a spur on the system output.
Sure, but having a sufficiently high frequency makes it relatively easy
to clean up, as well as it should be reduced by normal loop filtering
and oscillator integration.
Cheers,
Magnus
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