[time-nuts] Choke Ring Pictures

Bob Camp lists at rtty.us
Sun Mar 14 23:38:44 UTC 2010


Hi

Get a piece of polyethylene sheet (10 mill?).  Cut a piece (or three) and put it under the bottom of each plate. Put the set of them in the oven to bake. Probably put some weight on the inner pan. At some magic temperature the poly will melt and flow to fill the gap between pans. It's got good enough dielectric properties at L1 to make a pretty good dielectric "plug" for the  small gap. I suspect the same is true of the anodize on the pans.

Once it's out of the oven, pop rivet or bolt it all to the mounting plate. 

I suspect this is one of those things you try for the first time while the rest of the family is conveniently away at the movies  and there's a couple of hours available to air out the house before they get back ......

Bob


On Mar 14, 2010, at 5:42 PM, Magnus Danielson wrote:

> 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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