Thanks for the clarification.

I'm not entirely convinced that the ammeter is the best idea. There are
enough internal wires and coils to introduce a real possibility of error
when in close proximity to an inductor. It shouldn't be as much of a
problem with a toroid, but I'm still a little leery. I agree it would be
difficult to do the measurements well with a scope anywhere but at the
base of the antenna. Current probes and a detecting meter might be ok,
but you'd have to take a lot of care to avoid making an unintentional
loop which would couple to the inductor, and you'd have to calibrate the
potentially nonlinear detector. Phase information would be lacking, too.
I'm waiting for Cecil's response, since by his theory, as I understand
it, we should be able to get a decent phase shift through an inductor at
the base of an antenna providing the antenna is significantly longer
than a quarter wavelength. And if I understand your theory, we should be
able to see a full 30% change in magnitude and 45 degree change in phase
in the current through a base mounted inductor, if it's loading a 45
degree radiatior to resonance. Am I correct? I could measure that with
the same setup but with an antenna removed from the mount. And 30% and
45 degrees should be much easier to resolve with any accuracy than the
2.5 or 5 percent you predict for the setup I did measure.

Incidentally, I take it that your prediction for the setup I did measure
includes an 18 degree phase shift of current from input to output of the
inductor?

Roy Lewallen, W7EL

Yuri Blanarovich wrote:
I apologize. I read and was referring to the same quote, and interpreted
it to mean that the first measurement was made with the coil at the base
of the antenna. So where was it -- 78" from the bottom?

Roy Lewallen, W7EL




Yes,
mast 78" - coil - 38" top whip
we keep saying, looking at typical mobile antenna with loading coil about 2/3
up the quarter wave radiator. The lower the frequency, more loading, more
pronounced effect.

Caution, using toroid current transformers with scope leads would detune the
antenna setup and introduce errors. You can get away with this at the base, but
any stray capacitance up the radiator will detune it and skew the results.
Need to use thermal RF current ammeters or current probe with detector and
small meter together, no wires.

Yuri, K3BU