[time-nuts] Cheap Rubidium

Bob Camp lists at cq.nu
Thu Dec 24 14:37:51 UTC 2009


Hi

THe problem with cooler chips is that the heat still has to go somewhere. On the "other side" of the device you need to deal with both the original 10 or 20 watts plus the heat from the cooler. To move 10 or 20 watts and get a significant delta T you need a pretty big cooler chip. Since they are low voltage, that gets you right back to lots of current and thus magnetic fields. 

The idea of putting the cooler a distance from the cell and coupling with moving air is still an option though. 

Bob


On Dec 24, 2009, at 9:28 AM, Steve Rooke wrote:

> I wonder how peltier devices would work for this application. Coupled
> with a temperature feedback servo they could be used to heat/cool the
> rubidium. Does anyone know if they have any electromagnetic field
> issues with them, the ones I have seen seem to be completely enclosed
> in aluminium which should act as a Faraday cage. They have the
> potential of providing a large thermal transfer capability compared
> with passive devices.
> 
> 73,
> Steve
> 
> 2009/12/25 Joe Gwinn <joegwinn at comcast.net>:
>> 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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> 
> 
> 
> -- 
> Steve Rooke - ZL3TUV & G8KVD
> A man with one clock knows what time it is;
> A man with two clocks is never quite sure.
> 
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