[time-nuts] Cheap Rubidium

Bob Camp lists at cq.nu
Thu Dec 24 14:33:32 UTC 2009


Hi

A shorted tightly twisted pair of heater wire has a *very* low magnetic field. That goes double if you get cute with the way you lay the heater down. I have been told that kind of heater does indeed detune a rubidium. What ever you do, it needs to have a near zero field. 

Bob

On Dec 24, 2009, at 8:53 AM, Joe Gwinn wrote:

> At 10:06 PM +0000 12/23/09, time-nuts-request at febo.com wrote:
>> Date: Thu, 24 Dec 2009 09:46:13 +1300
>> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>> Subject: Re: [time-nuts] Cheap Rubidium
>> To: Discussion of precise time and frequency measurement
>> 	<time-nuts at febo.com>
>> 
>> Joe Gwinn wrote:
>>>> Date: Thu, 24 Dec 2009 08:57:42 +1300
>>>> From: Bruce Griffiths <bruce.griffiths at xtra.co.nz>
>>>> Subject: Re: [time-nuts] Cheap Rubidium
>>>> To: Discussion of precise time and frequency measurement
>> >> <time-nuts at febo.com>
>>>> 
> 
> [snip]
> 
>>> >> Distributed heating using wire wound or printed heaters perhaps, but to
>>>>> reduce the associated magnetic field bifilar winding should be
>>>>> considered.
>>>> 
>>>> Non-inductive power resistors, which are commercially available, have
>>>> very low magnetic fields.
>>>> 
>>>> The low-inductance resistors have Ayrton-Perry windings, which are
>>>> bifilar.
>> 
>> No, Ayrton-Perry windings arent bifilar.
>> 
>> Classically a flattened helical winding was made on a insulating card.
>> An identical winding was then wound in the opposite direction on top of
>> the first winding and the 2 were connected in parallel.
>> The idea being that the small magnetic field produced by one flattened
>> helix is cancelled by that of the other flattened helix.
> 
> True enough - while there are two conductors, they are not close and parallel.
> 
> Anyway, the point is that non-inductive components by definition have low magnetic fields, and that non-inductive power resistors are common.
> 
> To eliminate the field from the loop of resistors, one can have a linear string of A-P resistors in series, with a pair of return wires in parallel, with the return wires on either side of the resistor string, thus reducing the effective loop area.
> 
> Joe
> 
> 
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