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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