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[TowerTalk] Modeling

To: <>
Subject: [TowerTalk] Modeling
From: (
Date: Mon, 4 Feb 2002 10:06:59 EST
In a message dated 2/4/02 8:08:46 AM Eastern Standard Time, 

>  Modeling as to the optimum spacing and antenna elements/spacing is VERY
>  accurate for predicting patterns and front-to-back, especially when you are
>  a perfectionist as far as building antennas EXACTLY to the proper specs 
>  the proper materials.
>  Modeling as to the best heights for antennas for a particular wave angle 
>  a phased array is INCREDIBLY valuable!

At first, I was skeptical about antenna modeling software especially after 
some pros in art of using soft modeling could not answer or model some 
special situations I came across while playing with hard models on 2m antenna 
test range.
    When I got my W7EL EZNEC and K6STI AO, and started to understand how the 
software works and what are the limitations, I got to appreciate the power 
and potential of them (like savings looong nights of shuffling real elements 
on the real booms). They allow to study various designs under the same 
conditions (ground, height, phasing, dimensions). They give you idea as to 
parameters of the antennas (impedance, SWR, gain). But you have to be aware 
of some problems, that are mentioned in the documentation. There are some 
limitations, like insulated antenna wire, dissimilar metals, capturing the 
real ground quality and conditions, close proximity to ground.
    If we are aware of the limitations, we can properly use the software to 
optimize the arrays. I was very happy with modeling arrays for the ocean 
front QTH, I achieved very close results between soft models and real life.
    One test how good software is the verification of one of my findings (BMV 
rule #007) while hard modeling Razors: "Antenna has to be designed/optimized 
for the height in which it will be installed." When I changed height of the 
design antenna and reshuffled the spacing, I would get better performance 
(gain or F/B/S). This can be verified by using AO, changing height and 
running optimiZe. This is of course more pronounced at lower heights.
    One disturbing trend is seeing some antenna "designers" relying strictly 
on software and making whole new antenna design science based on what the 
soft modeling produces. There are still many factors that software does not 
include in calculations and the final test should be done by hard model or 
real life tests and comparisons with other known "standards."
    Don't forget the propagation modes and angles. Antennas have to be able 
to radiate and extract signals with maximum efficiency. That changes with 
sunspots and atmosphere (ionosphere) height. What plays well at sunspot max, 
will not play the same at sunspot min. 
    I saw dramatic difference between OK1RF fixed high stack on 10m and OK2RZ 
switchable multitude of antennas. At the beginning of the opening to Eu, 
OK1RF was S9, while OK2RZ was in the mud, barely audible. After about an hour 
into the opening, OK1RF about S6 (like them dipolites) and OK2RZ one of the 
top signals S9+20. OK1RF might have been again S9 at some other fringe. This 
illustrates BMV contester rule #001: "You never have enough antennas." The 
more of various (performance, angles, directions) antennas you have, the more 
various propagation conditions you can cover and take advantage of, the more 
points you can make.
    Antenna modeling software is a tool, just like an ax you would use to 
chop the wood, but not cut the meat on your plate. You can do that too, but 
you have to be aware of limitations. 
    About "multi-monobanders?" Term to distinguish "serial" monobanders 
(separate elements and feedlines) in a row on the same boom vs. "parallel 
monobanders" (tribanders, interlaced monobanders). Makes sense to me.


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