[time-nuts] Cheap Rubidium

[Bob Camp]

Hi

If that's what they are doing, it's going to have a lot more mag field than a twisted pair winding. I already know that twisted pair has enough field to make trouble ....

Bob


On Dec 23, 2009, at 3:46 PM, Bruce Griffiths wrote:

> 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>
>>> 
>>> Bob Camp wrote:
>>>> Hi
>>>> 
>>>> So if I want to set up 4 uncorrelated systems, that would require 20 tons of
>>>> water split into 4 tubs. Each tub would be roughly 3' x 4' x 15'. Of course
>>> > if they are all in the same basement, I still have a correlation problem. My
>>>> guess is that no matter what I do, any system that controls all the systems
>>>> the same way will run into correlation.
>>>> 
>>>> Oils, silicon fluids, and the like mostly hold less heat than water so the
>>>> tubs would get bigger. Maybe a few tons of mercury...
>>> Try about 145 tons of mercury per rubidium source as the specific heat
>>> of mercury is about 1/29 that of water.
>>> The redeeeming feature is that it will only occupy about 2.14x the volume.
>>> The specific of some oils may be as large as 1/2 that of water however
>>> the density is around 10-20% lower.
>>> 
>>>> Active heat control and a rational heat sink is sounding like a better
>>>> approach...
>>>> 
>>> 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.
>> 
>> <http://www.token.com.tw/resistor-pd/power-resistor-ah.htm>
>> 
>> 
>>> The major limitation is that the 25W or so dissipated by the rubidium
>>> source has to be transferred to ambient without raising the rubidium
>>> temperature too much.
>>> This limits the maximum thermal resistance between the baseplate and
>>> ambient that can be safely used.
>> 
>> I would be tempted to regulate temperature by actively controlling the speed of the fan (or pump) driving air (or oil) through the heat sink, as has been suggested.
>> 
>> Joe Gwinn
> Bruce
> 
> 
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