[time-nuts] Cheap Rubidium

Bob Camp lists at cq.nu
Thu Dec 24 20:25:51 UTC 2009


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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