Practical_Antenna_Handbook_0071639586

C h a p t e r 2 5 : A n t e n n a M o d e l i n g S o f t w a r e 557
• Terrain analysis examines the effect of nearby (i.e., within a few miles) topographic
features using principles of optical reflection and diffraction. In some countries,
government or private topographical databases can be downloaded for
automatic use by the software. If this is not the case in your country, manual
entry is always possible. Terrain analysis is of great benefit when utilized prior
to determining the height or location of antennas and their supports on a
specific parcel of land, but it is probably of most benefit when used even earlier
to compare the relative merit of multiple candidate sites for an antenna facility.
• Ionospheric propagation programs carry the ball the rest of the way, providing
statistical predictions of optimum working frequencies, the probabilities and times
for communicating between two points at any given time of the day, and the
propagation modes providing the most efficient path between those points. In
addition, some will predict received signal levels at distant receiving locations
anywhere on the globe for a given transmitter power level.
See Chap. 2 (“Radio-ÂWave Propagation”) for additional information regarding
these software tools.
Summary
Despite a plethora of caveats, “gotchas”, rules, and guidelines for users, today’s accurate
yet inexpensive modeling tools are a boon to antenna experimenters everywhere.
Hours or even days that might previously have been spent trudging through swamps,
prickly brush, or deep snowdrifts to erect yet another configuration of wires atop the
trees can now be put to better use, thanks to the power of the modern personal computer
and the considerable efforts and accomplishments of a dedicated group of scientists,
engineers, hobbyists, and entrepreneurs.
Many examples of antenna modeling results from both EZNEC (for the PC) and
cocoaNEC (created by Kok Chen, W7AY, for the Mac) can be found in the chapters of this
book dedicated to specific families of antennas. Any errors in the results presented are
the fault of this author, not the software packages or their authors.
See App. B for a list of antenna modeling software vendors and the link for obtaining
an NEC-Â4 license (U.S. users only).