[time-nuts] Choke Ring Pictures

Magnus Danielson magnus at rubidium.dyndns.org
Sun Mar 14 21:42:46 UTC 2010


Joe Gwinn wrote:
>>
>> Date: Sun, 14 Mar 2010 21:09:00 +0100
>> From: Magnus Danielson <magnus at rubidium.dyndns.org>
>> Subject: Re: [time-nuts] Choke Ring Pictures
>> To: Discussion of precise time and frequency measurement
>>     <time-nuts at febo.com>
>> Message-ID: <4B9D425C.2050307 at rubidium.dyndns.org>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> Bob Camp wrote:
>>>  Hi
>>>
>>>  Wedding cake pans normally come in 1" increments and are either 2" 
>>> or 3" deep. Sets are 2" increments on the diameter:
>>>
>>>  http://cooksdream.com/store/wedding-round.html
>>>
>>>
>>> http://www.hubert.com/store/products.asp?CAWELAID=126235277&A=SB%2E58369%2E10738&Dn=0&An=966+966&Au=Presentation+Id&Ntt=10738&N=966+966&src=chanadv&Ntx=mode+matchall&D=10738&Ntk=SKU 
>>>
>>>
>>>  The height would be fairly easy to adjust. The diameter not so much so.
>>>
>>>  Looks like 2 and 2.5" are typical dimensions for the depth. ~1" 
>>> looks pretty typical for the width. A 2" deep / 2" diameter step set 
>>> looks like it would do a pretty good job . It won't be accurate 
>>> enough to be perfect. Without a 3D EM program it would be tough to 
>>> figure out just what the errors would do to you.
>>
>> With 2.5" depth and 14", 12", 10", 8" and 6" diameter pans you are not
>> completely in a different world from some antennas:
>>
>> http://facility.unavco.org/project_support/permanent/equipment/antennas/ant_cals.html 
>>
>>
>> Evaluating the performance may be a different thing.
>>
>> One thing to care about is the leakage between the pans if you just 
>> stick them inside each other.
> 
> I'd be tempted to use EMI gaskets between the pans, except that contact 
> will soon be lost as the aluminum grows a nice oxide layer. But it may 
> not be necessary to make DC electrical contact, as the capacitance 
> between the metal layers may suffice to act as a short at 1.5 GHz.  A 
> thin sheet of mylar (or a heavy anodization layer) between would help 
> this along, by increasing the capacitance.

However it is done, you want it to be fairly stable. Evenly distributed 
screws against a stable platform like a steel-plate should do it.

An alternative is to TIG them together.

Cheers,
Magnus




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