[time-nuts] Cheap Rubidium
lists at cq.nu
Thu Dec 24 20:55:23 UTC 2009
Every time I've tried the coli thing, field uniformity has become an issue. I'm also not real sure just how stable multi axis mag sensors are.
If I had a bunch of mu metal sitting in the basement I'd certainly use it in the setup. Last time I checked the stuff was not cheap ....
On Dec 24, 2009, at 3:50 PM, Bruce Griffiths wrote:
> 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.
> Bob Camp wrote:
>> 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 ....
>> 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
>>> Bob Camp wrote:
>>>> 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.
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