Tom,

OK, I tried what you suggested. I put my loading coil midway up a 20ft
vertical wire in the EZNEC model. I reduced the number of turns to
lift the resonant frequency to 5.6MHz. EZNEC predicted that the
magnitude of the current at the top of the coil would be 77% of the
magnitude at the bottom.

Then I removed the coil in the model, replaced it with a straight wire
containing an EZNEC lumped load, and adjusted that load for antenna
resonance at 5.6MHz again. I needed +j1630.

Given the dimensions of the coil, the Corum calculator predicted a
lumped circuit equivalent reactance of +j1573, and it predicted a
current fall-off across the coil of 78%.

73,
Steve G3TXQ


On May 9, 5:35*pm, K7ITM wrote:

Steve, this is fine for a base loading coil, but I'd suggest you try
your experiment with a loading coil well up the antenna, where the
coil is significantly larger diameter than the straight conductor in
which it's placed. *The same size coil you described (though
presumably a different number of turns), placed at least half way up
something like a 15 or 20 foot long thin wire, should illustrate the
point. *Is the EZNEC model then in such good agreement with placing a
reactive load at that point in the antenna, where the reactance is
from ON4AA's online calculator?