Gary Schafer wrote:

When the measurements of the coil were done on the bench it seems that
it was done with 50 ohms in and 50 ohms out. That hardly seems like it
would give the same information as when the coil was in actual use as
an antenna loading coil.

A bench test is fine. An inductor is an inductor.

The only problem with a bench test is simulating the load impedance
presented by the antenna and of course strong local fields generated
by the antenna are missing, but the actual error can be reasonably
small.

However, inductors were measured in an actual antenna. I measured
current, and Roy Lewallen measured phase and current.

I couldn't measure time delay or phase in my actual antenna because I
was measuring a mobile antenna. There wasn't any way to measure phase
without perturbing the system and rendering any data unreliable.

This long painful thread (it's been going on years now) started because
K3BU claimed a loading inductor had most of the current in the first
few turns. I made some measurements
and posted them at:

http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

These measurements show exactly what anyone who understands loading
coils would expect, that it is stray C in comparison to load impedance
on the inductor that determines any current taper, and that for a
reasonable sized inductor the taper is very small.

I wrote a description at:

http://www.w8ji.com/mobile_and_loaded_antenna.htm

I can't see anything in there that needs changed, based on what I've
read here in this thread.

Rather than a 50 ohm load how about if a load was placed at the end of
the coil to simulate the antenna, a resistor and capacitor to take the
place of the antenna impedance and reactance. Then measure the current
in and out and the phase shift.

I've done that also.

You are absolutely correct Gary, it is possible to come very close with
a lumped load on the inductor *except* of course the surroundings are
different.

The inductor test fixture I normally use is a large copper box made
from blank double sided PC board sheets. It has vacuum caps (very high
Q) and various detectors and probes.

I have to characterize large inductors on occasion as part of designing
RF systems. It's less scary than turning on a 50kW PA and having things
misbehave at full power, or building a phasing system or phasing/ATU
combo that doesn't work.

73 Tom