Topband: Measure Choke Impedance

[Ford Peterson]

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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