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
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