Reg Edwards wrote:
The input and output currents of a loading coil of finite length are always
different from each other.

There's hardly any "input and output currents" for a loading coil in
a standing wave antenna. That concept is why W8JI is in trouble with
his explanations. What is actually being measured is the magnitude
of the standing current wave.

There is forward current flowing into the bottom of the coil and out
the top. There is reflected current flowing into the top of the coil
and out the bottom. The net current is a standing current wave. If we,
as Kraus suggests, assume that the forward current equals the reflected
current (relatively small error in doing so) then there is zero net current
flowing in and out of the coil. The standing wave current is, well, just
standing there and is not "going" anywhere.

The gross error that a lot of people are making is that standing
wave current flows. If the forward and reflected currents are equal,
as Kraus assumes for purpose of discussion, then there is zero net
current flow through the coil. Yet, net current is what everyone
is measuring. What they are actually measuring is the value of
the standing wave current at each end of the coil and it is not
flowing. It is only an artifact of the superposition of the two
waves that are flowing.

The magnitude of the reflected current can be estimated from the
feedpoint impedance. The lower the feedpoint impedance, the closer
in magnitude is the reflected current to the forward current. For
a center-loaded mobile antenna, the reflected current through the
coil appears to be well within 5% of the value of the forward
current.
--
73, Cecil http://www.qsl.net/w5dxp


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