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[TowerTalk] Ant Modeling (long)

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Subject: [TowerTalk] Ant Modeling (long)
From: (Pete Smith)
Date: Fri, 18 Jan 2002 05:43:58 -0500
I won't retrace the ground that K1TTT has already covered, but just want to
add a few points.

The computer codes that are used for modeling (currently NEC-2 and NEC-4 in
amateur circles) have been fairly well verified aganst range data,
including the famous helicopter tests by WA3FET and others.

All of these modeling methods have specific limitations -- circumstances
they don't model well, or special precautions that need to be observed in
particular situations.  I think it is equally important to be sure that a
particular model has converged -- that is, breaking up the antenna into
shorter segments does not produce major changes in the gain or pattern.
I've been bitten by THAT one a few times.

For real-world terrain, you definitely need to combine antenna modeling
with terrain modeling (YT or TA).  When it comes to interactions with other
antennas, I have found it useful to maintain a model of my entire station
(including tower and guy wires as well as antennas).  I'm convinced this
has saved me a few times from making changes that would have had undesired
side-effects on other antennas in the mix.  The only problem with EZNEC in
this application is that its 500-segment limit is easily exceeded on the
higher frequencies. 

And finally, it's worth mentioning that ARRL offered to accept gain and
pattern claims in antenna advertising a couple of years ago if
manufacturers would submit NEC-4 models of their antennas for verification. 

73, Pete N4ZR

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