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[TowerTalk] "Ground" planes

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Subject: [TowerTalk] "Ground" planes
From: (L. B. Cebik)
Date: Thu, 22 May 1997 12:33:07 -0400 (EDT)
I have been playing with models of ground planes for some time--and also
capacity hats--all of which has given me some strange ideas about the two.
I hinted at the route of analysis I am taking is a note at my site about
ground(s).  Well, the note is now part 1 of a new series on "a modeling
perspective on ground planes," and the first 4 out of 5 sections are in
place. (See the URL in the signature line below.)  NEC-4 permits wires
underground (with restrictions), and that permits models to be run
from free space to subterranean levels in a continuous series of steps
(using the Smmerfeld-Norton ground only)--and that has helped overcome
some of the older modeling limitations that only approximate uncertainly
what happens with a buried plane.  Will try to get the last part done and
up before next week, but choring could take its toll.

Main lesson:  if you want 6 dB extra gain from your vertical, move it from
middle US to a Caribbean island--but vertical users all know that.

Secondary lesson:  it is possible to make an effective buried plane with
wires only about 0.14 wl long.

Tertiary lesson:  the free space feedpoint impedance (which holds good
down to at least 1.5 wl up) of a resonant 1/4 wl main element and plane is
not 35 ohms (or even thereabouts), but more like 22-23 ohms, no matter how
many radials one adds.  And that raises lots of questions about VHF
vertical antenna designs.

Unfortunately, there are a bunch of preliminaries to go through before
these curiosities emerge, but perhaps they will be curious also--I could
not simply throw out a bunch of tables without letting you know how my
thinking on the subject works and how the models got constructed for
reasonably decent reliability.

Hope the notes are useful to someone.



L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
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