John Popelish wrote:

You two are so close to agreement. Standing waves have a current that
varies with position. The fact that the EZNEC simulation of a loading
coil shows differing current in a situation that is a fairly pure
standing wave situation (more energy bouncing up and down the antenna
than is radiating from it) means that the RMS current will vary along
the standing wave. And, since the simulation shows a different current
magnitude at the two ends of the coil, a significant part of a standing
wave cycle must reside inside the coil (more than the physical length
between the two ends of the coil would account for).

No, you're misinterpreting what you're seeing. Imagine an LC L network
with theoretically lumped series L and shunt C. If you look at the
currents at the input and output of the perfect inductor, you'll find
that they're exactly the same. If, however, you look at the currents in
and out of the *network* you'll see that they're different, because of
current going to ground through the C. And, as I said before, you can
even pretend it's a transmission line and measure forward and reverse
traveling waves and a standing wave ratio. But with zero length, there
can be no standing waves inside the inductor. Yet the terminal
characteristics of the network are the same as a transmission line. You
don't need to imagine standing waves residing inside the inductor in the
LC circuit, and you don't need to imagine them inside the inductor in
Cecil's model, either.

When you look at the currents reported by EZNEC for the model on Cecil's
web page, the current at the top of the coil is the equivalent to the
*network* current described above. It's the current flowing through the
inductance minus the current being shunted to ground via the C between
the coil and ground. You can tell just how much this is by looking at my
modified model and subtracting the current going into the coil from
ground from the current going into ground from the added wire. They're
not the same -- the difference is the displacement current through the C
from the inductor to ground. When I removed the ground, you could then
see the current flowing through the inductor, by itself, without the
current being shunted off. And lo and behold, it's nearly the same at
both ends of the inductor, showing that the inductor is behaving very
much like a lumped L. Only in conjunction with the C to ground does the
combination mimic a transmission line -- just like any other lumped LC
circuit.

Of course, at some length and/or poorness of interturn coupling, a coil
will start behaving in a way we can't adequately model as a lumped L.
But that's not the case here.

. . .

Roy Lewallen, W7EL