Bart Rowlett wrote:
The currents through two nodes connected in series, without branches, is
identical. I think that fact was established before Kirchoff but it's
certainly stipulated in circuit theory.
Let's deal with concrete examples. Assume a lossless, unterminated
transmission line. Because of the standing waves, the net current
in that series loop varies from point. It is zero every 1/2WL and
in between those zero points, it is at a maximum. That's all I was
trying to say - that the series current in a distributed network
with standing waves is not constant because it no longer can be
considered a "circuit". It must be considered a network as it is
an appreciable portion of a wavelength. The phases of the forward
current and reflected current are rotating in opposite directions
which causes their superposition magnitude to vary from minimum
to maximum. The magnitudes of the forward and reflected traveling
wave currents can be constant while their phasor sum varies as a
standing wave sinusoid.
Most of the stuff in this posting is a diversion away from the original
argument which is: Does the current through a 75m bugcatcher vary from
end to end? Since the net current is the standing wave current in a
standing wave antenna, it is mostly standing wave current, not traveling
wave current. Kraus even suggests that we can consider the forward
current equal to the reflected current in a standing wave antenna
for purposes of conceptual discussion which means the net current
is not moving at all, i.e. not flowing into the bottom of the
coil and out the top as assumed by W8JI on his web page. Balanis
clearly states that a standing wave antenna can be analyzed based
on the forward current and the backward current.
Simulations with EZNEC using the helix option indicates that the net
current is not the same at each end of a bugcatcher coil. Essentially
the same result occurs using a series inductive stub.
--
73, Cecil
http://www.qsl.net/w5dxp
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