[TowerTalk] One off balun question

[Ray, W4BYG]

Steve and Jim,
Both of you gentlemen are recognized as very knowledgeable on the 
subject of chokes.

So for those of us looking for testing guidance in brief, what is a good 
way to determine the resulting impedance of a given choke at a 
frequency(s) of interest, given a MiniVNA or whatever method you suggest?

I have studied both of your online compositions in detail and am left a 
bit confused by all the dialog.  Can you summarize for us?
Ray, W4BYG

On 10/31/2014 12:10 PM, Steve Hunt wrote:
> 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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