>I would like to know from some of those who are active in modeling antennas
>what software is being used. If more then one source, what correlation
>issues have been observed.
-----
I am somewhat behind the curve, using NEC-2 based EZNEC+. I have other
programs available to me, but have little time right now with the demands of
running an active small business (www.highfrequencyelectronics.com if you're
curious) and developing a decent ham station at what I hope is my last QTH.
I might also note that I do not strive for precise mm-scale agreement
between models and as-built antennas. My use of modeling is primarily to
verify concepts at a general level, and identify behaviors and trends in
patterns and feedpoint impedances. Also, some of my biggest projects have
been in areas where the models are least reliable, e.g., the K9AY loop and
its connection to real ground, and Coupled-Resonator antennas (aka Open
Sleeve) with extremely close spacing relative to length. In both these
cases, my models were tweaked to fit the measurements, sometimes in
violation of accepted practice.
Most recently, I relied heavily on modeling to decide how to build my new
160M vertical. After exploring options, I settled on 100 ft of 25G,
series-fed, with a six-spoke top hat of #16 wire supported by 13-ft quad
spreaders from my boneyard. Modeling suggested that going beyond 100 ft. was
not a significant benefit, but anything less would need a larger capacity
hat and have a reduced VSWR bandwidth with a simple matching network. Also,
I was able to see the greatly increased loading by using a perimeter wire
connecting the ends of the capacity hat spokes. The measured zero-reactance
frequency is higher than modeled (1725 vs. 1670 kHz). This is easily
explained by uncertainty in choosing an equivalent diameter "solid wire" for
the 25G tower (I used 5 inches). Feedpoint reactance is quite close, but the
resistive component is higher than modeled, 45-50 ohms instead of 38-43 over
1800-1900. I did not see this with modeling of a previous inverted-L over
the same radial system, and so far, cannot find a set of realistic
parameters in EZNEC that forces the model to produce that impedance. Maybe
I'll figure it out later this year when I install and evaluate a large
buried radial system!
73, Gary
K9AY
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