[time-nuts] Cheap Rubidium

Joe Gwinn joegwinn at comcast.net
Thu Dec 24 13:53:12 UTC 2009


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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