NEC-LIST: Running AO models with NEC engines

The latest version of the freeware MultiNEC program includes the capability
of importing models that are in '.ant' format. This is the format that is
used with the K6STI AO and NEC/Wires programs. When these models are
imported into MultiNEC all symbolic expressions are preserved, all symbol
names are automatically converted to MultiNEC single character variable
names, and all units override specifiers are handled correctly. (But some
other AO model file features are not supported. For example, the
'Symmetric' command is ignored.)

Once the model has been imported you can view it using any of the supported
viewers and run it using any of the supported NEC engines, including EZNEC
standard, EZNEC-M pro, or EZNEC/4 pro; Nittany NEC-Win Plus, NEC-Win Pro, or
GNEC; or the included public domain NEC2 engine. No matter which engine is
used you can specify any type of ground, including "MiniNEC" ground (a
combination of Perfect and Reflection Coefficient grounds). You can also
use "split" sources to simulate a source placed at the very end of a wire,
such as the apex of an inverted vee. In many cases the use of split sources
lets you duplicate the MiniNEC convention of placing sources at segment ends
(pulses) even though NEC puts sources at segment centers (practically
speaking). Split sources are available no matter which engine is used.

Since NEC and MiniNEC will usually produce slightly different results you
may find that an antenna that was resonant under MiniNEC is no longer so
when run under NEC. You can use the MultiNEC "Resonate" function to find
the new resonant frequency. If the dimensions of the model have been
defined using symbols (aka modeling by equation) you can also use the
Resonate function to automatically vary the geometry in order to achieve
resonance at a desired frequency.

Even if you don't own one of the K6STI programs there are many .ant files
available. Several were included on the diskettes bundled with recent
volumes of the ARRL Antenna Compendium series. Also, Brian Beezley has made
available a free reduced-function version of AO called NF, for near field
analysis. The NF package includes dozens of models, most with very
instructive comments. (Search the web for "K6STI NF.EXE".)

Speaking of free reduced-function versions and instructive comments, EZNEC
models can also be annotated and Roy Lewallen has done so with all of the
sample models that are included with EZNEC. These comments, known as
Antenna Notes in EZNEC terminology, are now shown along with the wire
information when an EZNEC model is imported into MultiNEC. A free demo
version of EZNEC, including the complete user manual and several annotated
models, is available at www.eznec.com.

The latest MultiNEC release has several other enhancements, including
support for non-English language format numbers that use a comma as a
decimal separator. For more details and a free download file see
www.qsl.net/ac6la/. MultiNEC requires Excel 97 or later.

73,
Dan AC6LA

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