[TowerTalk] antenna modeling with NEC-WIN BASIC

[L. B. Cebik]

On Wed, 16 Sep 1998, Al Samson wrote:
> 
> This is the same software that I got in Joe Carrs third edition antenna
> handbook. Its the
> first one that I could understand and I highly recommend every one check it out.
> 
> Mark Lowell, N1LO wrote:
> 
> > Greetings,
> >
> >  I recently purchased the NEC-WIN Basic modeling software package from
> > Nittany Scientific.

This is surprising.  NEC-Win Basic is a Windows product using NEC-2 and I
am surprised that it is enclosed with a book.  The program uses a
spreadsheet format wire entry "page," with click access to entering
sources, loads, wire material, and wire size in pull-down boxes from the
page.  There are also facilities for scaling and rotating wires, which can
ease development of radial systems and the like.  Among the options are
transmission lines and networks (about the only first level program with
the network inputs enabled).  The pattern outputs permit multiple requests
for patterns, so you can specify both azimuth and elevation plots at one
time, although you might have to grow accustomed to the fact that it uses
theta or zenith elevation scales counting from overhead downward rather
than upward from the horizon--theta scales are native to NEC and simply
translated to elevation by other programs.  At the present time, NEC-Win
Basic is the only NEC-2 entry program written directly for the Windows
environment, although this may change by early 1999.  At present, other
available NEC-2 entry programs are written for the DOS environment (but
work fine in a DOS window and do not require rebooting to the DOS mode
unless you just want to do that).  There are, of course, other facilities
in NEC-Win Basic not mentioned here.

Nittany-Scientific has a web page at www.nittany-scientific.com, and you
can find web links to it and other vendors of antenna modeling programs at
the first antenna modeling entry on the index page of my site.  All NEC-2
programs are similar in that they all use a version of the basic NEC-2
core, which has many capabilities and some limitations.  The included
Sommerfeld-Norton ground calculation system provides more accurate results
for antennas with part or all of the structure below 1/4 wl, where the
MMININEC ground system loses accuracy.  (However, MININEC has some
abilities that are better than those of NEC-2--there is no such thing as a
perfect antenna modeling core, not even NEC-4.)  One limitation of NEC-Win
Basic is that it did not include (in the version I have) a means for
automatically calculating the Leeson equivalents for tapered diameter
elements, which is a feature included on some other entry level programs.
NEC-2, without the substitute constant diameter element, will show varying
degrees of inaccuracy with elements having different diameter tubing,
depending on the number of steps and their placement along the element.
(The substitute element is not just one having an average diameter of all
the tubes in the real antenna, but will have a somewhat different length
as well, since it is the electrical--not just the mechanical--equivalent
of the tapered diameter element.)  This limitation may be eliminated
around the first of the new year.

Final selection of a program depends on which one gives you the most
comfortable feel and includes the interface functions (input and output)
with which you can get the most info for your purposes.  Each one has some
unique capabilities, since each program writer tends to find ingenious
ways to make certain input work easier or find some useful way to present
output data.

These notes are written from experienece with virtually all of the
currently available NEC and MININEC programs (and a few no longer
produced).  I hope they are useful.  I cannot claim that any of the
programs have zero bugs, but I know that all detected ones have been
cleansed from all of the available programs so that test models yield
comparable results on all of them.  However, in comparing results between
programs, remember that there are dozens of input and out points requiring
rounding, and each implementation of NEC-2 does this in different ways at
different points in the string of calculations.  Hence, you may expect to
find differences in the last significant digit of any calculation
output--which is usually far enough down to make no operational difference
in the working antenna.

I hope these notes are useful.

-73-

LB, W4RNL

L. B. Cebik, W4RNL         /\  /\     *   /  /    /    (Off)(423) 974-7215
1434 High Mesa Drive      /  \/  \/\     ----/\---     (Hm) (423) 938-6335
Knoxville, Tennessee     /\   \   \ \   /  / || /      (FAX)(423) 974-3509
37938-4443     USA      /  \   \   \ \       ||              cebik@utk.edu
                URL:  http://web.utk.edu/~cebik/radio.html









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