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Old October 19th 04, 05:33 AM
Cecil Moore
 
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John Smith wrote:
"The loading coil acts as the lumped constant that it is, and disregarding
losses and coil radiation, maintains the same current flow throughout.


This statement is somewhat misleading. A standing-wave antenna is
somewhat like a transmission line with standing waves. There are
TWO component currents in a standing wave antenna, forward and reflected.
The total current is the phasor sum of those two currents. Even if the
forward current were constant and the reflected current were constant,
the total current changes because of the phase shift between the
forward current phase and reflected current phase as these two phases
are changing in opposite directions.

For instance, given a 1/4WL ground plane vertical, the forward current
and reflected current are in phase at the feedpoint, thus resulting in
high current. At the tip top of the 1/4WL ground plane, the reflected
current is 180 degrees out of phase with the forward current and their
phasor sum is zero at that point.
--
73, Cecil, W5DXP


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