[TowerTalk] One off balun question

[Steve Hunt]

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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