How can I test how well a choke balun is performing? I know how to test a
transformer balun, but am cluless as how I can compare several different
choke balun approaches.

One possible method comes to mind... use an RF current probe to see
how much RF is actually flowing on the outside of your feedline. I've
seen plans for such probes, made from a clamp-on ferrite choke core
and winding (making a simple RF transformer) plus a diode, cap, and
meter.

In order to distinguish conducted RF (which the balun would be
expected to be able to stop) from induced RF from the antenna itself
(which would probably go right around the balun) you might want to
try disconnecting the antenna itself from the output of the balun, and
substituting an equivalent resistance/reactance at the frequency of
interest. Push a few watts into the "dummy load", run the current
probe down the feedline from the balun to your rig, and see what the
peak current is. Repeat at multiple frequencies, and (if practical)
with different feedline lengths. Using a half-wavelength-long coaxial
feedline would probably maximize the sensitivity of the test, as it
would present a low RF impedance on the outside of the coax at the
"bottom" of the current balun.

Repeat with other current baluns and compare.

To be complete, I suppose that you'd also want to measure the
temperature of each balun before and after a high-power test, to try
to get some feeling for the amount of loss in the balun itself.

--
Dave Platt AE6EO
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