I think not only the dielectric constants around the coax shield but also the
conductivity of the core influence the result.
Hans - N2JFS
-----Original Message-----
From: Steve Hunt <steve@karinya.net>
To: towertalk <towertalk@contesting.com>
Sent: Fri, Oct 31, 2014 12:10 pm
Subject: Re: [TowerTalk] One off balun question
Jim,
If I wind exactly the same number of turns of the same cable with
identical spacing on the same-size toroids, but use two different core
materials, I get very different values of equivalent C. The only thing
that is different is the core material.
I initially thought the dielectric effect of the core material might be
the significant factor; but as an experiment I built a parallel-plate,
circular, capacitor with the toroid fitted between the plates, and
didn't measure much change in capacitance with different mixes.
Steve G3TXQ
On 31/10/2014 15:17, Jim Brown wrote:
> On 10/31/2014 3:50 AM, Steve Hunt wrote:
>> If we had a good way to predict C, predicting the CM impedance of a
>> particular choke design would be relatively straightforward.
>
> Variables include the turn spacing, the diameter of the choke,
> diectric constant of the cable outer insulator, the dielectric
> constant of the core material, and the portion of the winding
> influenced by both. The dominant parameters are those associated with
> the windings and the air dielectric. You can see this if you study the
> graphs of 1-14 turns of small wire for the various core materials done
> by my anonymous collaborator nearly 10 years ago. He chose to be
> anonymous because he works in a well equipped scientific lab in a
> major institution, and needs to avoid professional jealousies. :)
>
> 73, Jim K9YC
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