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Old February 14th 14, 12:08 PM posted to rec.radio.amateur.antenna
W5DXP W5DXP is offline
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First recorded activity by RadioBanter: Jul 2011
Posts: 182
Default The ATU, a dying art?

On Thursday, February 13, 2014 11:09:51 PM UTC-6, wrote:
Is this related to the great K3BU-W8JI "current across the coil" debate?
Seems some came to the conclusion that the location of the coil had a
lot to do with whether the current was equal at each end of the coil..
IE: in one exact location it could be equal, but in other locations it
could vary at each end.


It is related. I wasn't trying to revive the debate - just trying to pick
Sal's brain for his technical opinion.

The total current in a 75m loading coil, like any other standing wave
antenna, is primarily a function of the superposition of the forward
current and reflected current. The total current is highest when those
two currents are in phase and lowest when those two currents are 180
degrees out of phase. The actual energy decrease in current is minor
compared to the effect of phasing. One can assume zero energy decrease
in the individual forward and reflected currents and still be very close
to the measurements of the actual total current.

Strangely enough, both sides of that argument were half-right and
half-wrong. K3BU's argument that the coil replaced all of the missing
part of the antenna was about half right. W8JI's argument that a
phase shift between the top of the coil and the stinger was responsible
for all of the missing part of the antenna was about half right.
--
73, Cecil, w5dxp.com