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[TowerTalk] EZNEC

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Subject: [TowerTalk] EZNEC
From: (L. B. Cebik)
Date: Sun, 7 Dec 1997 17:43:07 -0500 (EST)

I assure you that we are concentrating on what is wrong with the model.
Nothing is.  Possibly, you have not added in wire loss, but the difference
would be insignificant relative to copper or aluminum.  I have run the
very models you speak of and get the same results--and the results are
valid.  I use them on EZNEC (NEC-2) and EZNEC Pro (NEC-4), as well as on
NEC-Win Pro (NEC-2) and GNEC (beta of NEC-4).

I even doubled and quadrupled the number of segments per wire to bring the
feedpoint closer to the junction of the vertical and the radials, since
NEC places the feedpoint in the middle of the segment (actually
distributed along that segment) to which it is assigned.  Moreover, I also
used the well-known EZNEC tapering feature to make the feed segment very
short, bringing the feedpoint even closer.  No significant difference.

I assure you that, as a modeler with some experience with the span of
available modeling programs, that there is nothing wrong with the model
and that the results are in accord with antenna theory and that NEC-2 is
in no way inaccurate with this model relative to the more advanced NEC-4.

It might be useful for you to examine all lobes and nulls of your dipole
to look at the far field figures for the dipole.  Even your chart shows
the higher gain at higher elevation angles for the dipole, and hence its
susceptibility to higher angle radiation.

You may also wish to question your supposition that a vertical is "far
superior" to a dipole at 1/2 wl up.  Each antenna enjoys some points of
superiority when the dipole is 1/2 wl up.  The question is what makes one
superior in this or that specific aspect relative to specific operating

Using your own model with radials, you may undertake several exercises of
use in getting used to the modeling program.  One is to raise and lower
the assembly from just above ground (perhaps a few cms) to perhaps rooftop
height (about 1/2 wl) and examine the pattern strengths and angles.
Another is to change the ground conditions under the antenna and in the
more distant ground that affects the far field patern (using a single
ground medium will do the job).  You may also wish to create a vertical
dipole and examine its properties at various heights over various types of

Once more, you have done nothing wrong with these models, and there is
nothing wrong with the program you are using.

At my web site, there are a few notes that others have found useful in
getting started in modeling.  While they do not directly address the
issues with which you are wrestling, they may be of some use along the

Good luck.



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