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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