[TowerTalk] One off balun question

[Jim Brown]

On 10/30/2014 3:22 AM, Jim Thomson wrote:
>   I realize the uh, measured at low freqs tells me little about the CM Z of a choke.  I was just interested to know how much uh you folks are seeing on these bigger  CM chokes, where 5-15 turns of coax are used
> on 4-8 cores, that type of scenario.

Hi Jim,

Values of parallel R, L, and C can be computed from the plots of choking 
Z using conventional curve fitting.  Rp is the measured Z at resonance 
(the peak of the curve), L can computed from the slope of Z curve at low 
frequencies, C can be computed as the value that resonates at the peak 
frequency with L. I go one step further and put those values in a 
spreadsheet, plot the impedance of that network on the scale as the 
measured data, and tweak values for best fit.

This method is based on materials like #43, which have only one 
resonance. #31, which has two resonances, requires more reliance on 
curve-fitting. #31 with a lot or turns is like a double tuned IF. I 
discuss this in the tutorial).

Thus, C is that which matches curve on the higher frequency side of 
resonance, the value of L near resonance is that which resonates with C, 
and the value of L at low frequencies is that which matches the slope of 
the curve well below resonance. Values obtained are a fair approximation 
of what might be obtained from more detailed curve fitting.

73, Jim K9YC