[TowerTalk] Test Fixture for Common Mode Chokes

[Jim Brown]

BUT -- what I forgot to add that the ENGINEER in me realized that choke 
designs will be used with feedlines in all sorts of lengths, so my 
design goal was to make the resistive component of the choking Z 
sufficiently large that it would dominate the Z, inserting a near open 
into the common mode circuit at that point. That's why using a resistor 
equal to that value as a load is useful as a first approximation. And, 
of course, because it's a parallel resonant circuit, we know that the 
value of that resistance will fall as we move away from resonance. These 
concepts were developed in tutorials I've written about chokes and their 
use.

73, Jim K9YC

  1/24/2026 1:43 AM, Jim Brown wrote:
> A better approximation would be provided by adding the parallel resonant 
> equivalent circuit of the choke, computed empirically from the measured 
> impedance curve. One of my more valuable EE courses was freshman year to 
> develop equations like this.