Fw: Re: [TowerTalk] News from Bencher

[L. B. Cebik]

>Neat idea, but I'm not sure the trapped antenna guys would agree.  Good
>models of trapped antennas (not to mention linear loading) seem to be
>pretty tricky.  For that matter, NEC-2 has trouble with modeling the C-3
>type of driven cell -- does NEC-4 do it any better?

Actually, NEC-2 and NEC-4 are about on a par when it comes to close spaced
elements of dissimilar lengths and/or diameters--at least according to the
research I did for the NEC-4 limitations article in QEX.

Whenever I have reason to suspect that the spacing of dissimilar wires is
reaching the critical threshold, I do two things--1. run the average gain
test, which will show up this problem (available on NEC-Win Plus andon
EZNEC 3.0) and 2. model the system on MININEC.  For very complex overall
antenna designs, I may isolate the feed system as a model and compare the
results to MININEC results--since MININEC has a lower overall segment
(pulse) limit.  MININEC is not limitated in the same ways as NEC, which
makes it useful on occasion to cross check between modeling cores.

-73-

LB, W4RNL

L. B. Cebik, W4RNL         /\  /\     *   /  /    /    Tel: (865) 938-6335
1434 High Mesa Drive      /  \/  \/\     ----/\---    http://www.cebik.com
Knoxville, Tennessee     /\   \   \ \   /  / || /    e-mail: cebik@utk.edu
37938-4443     USA      /  \   \   \ \       ||     e-mail: w4rnl@arrl.org





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