I am following the thread discussing the actual "impedance" of a choke. The
calculations are fine. How do you measure such a thing?
I have been using the method described in Walt Maxwell's book Reflections
II. You take the balun and present a mismatched load over a ground plane
(he used an aluminum plate, I use copper clad tin). I use my Autek VA-1 to
generate some suitable RF and a high impedance scope probe to measure the
voltage at each 1/2 of the load (usually simple resistors of known value at
RF--I use 100ohm and 50ohm for simple calculations).
Using Excel, I load the voltages at each resistor (at frequency of course)
and calculate the currents passing through each for every ham band of
interest. I then compare the currents (A/B) and compute a "figure of
merit." A perfect balun is 100%.
Using several techniques for "choking" action, I can get >95% accross the HF
bands using any one of several methods. (beads, wound toroids, etc.)
Frankly, I just keep adding turns until I get good results on 160 and
subtract turns if the low end looks good and 10 meters falls apart.
Is this a good approach or am I missing something?
Ford-N0FP
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