Longmont Amateur Radio Club - Colorado

ANTENNA MODELING

Antennas, their construction and performance continue to be of great interest to Hams. While the physics and math required to design antennas exist they can require more time and effort than is available to most hobbyists, there is a large amount of readily available antenna modeling tools that make performance prediction much less time consuming.

Modern modeling software finds its origin in Numerical Electromagnetic Code (NEC) developed in the 70’s. There are several versions available, and the source code for NEC itself is has been made public. A recent Goggle search produced 160,000 hits, one of which, “The unofficial Numerical Electromagnetic Code (NEC) Archives http://www.si-list.net/swindex.html”, is a good place to get started.

L. B. Cebik, W4RNL has done extensive research and written many papers and books, his web site www.cebik.com, is an excellent resource.

I have used several and am currently using EZNEC by Roy Lewallen. See, http://www.cebik.com/model/nec.html, and http://www.eznec.com/.

Roy has made a version (3.0 I think) available with the 20^th edition of the ARRL Antenna book, and sample files are available for just about every conceivable antenna type.

A particularly good application of modeling software is to predict the radiation pattern of real world antennas. Most of us can’t put a 75 meter dipole at 150 plus feet so what will one do at 30 feet, over clay soil.

We will model several common types (including the G5RV the club will use for Field Day) during the Hints and Kinks segment of the next several club general meetings.

Bob, WA2EKU (LARC Vice President)