Modeling Loads and Transmission Lines

L. B. Cebik, W4RNL

Questions often arise about how properly to model loads and transmission lines within various versions of NEC and its commercial implementations. So I thought a brief primer might be useful. The utility of a primer is unquestionable, but that it can be brief quickly proved false.

Although the information is covered in both the NEC manuals and the instruction manuals that accompany commercial implementations, something more systematic seems needed--something with examples carried from one level to another so that users can see the transitions and get a sense of what is and is not possible--and how to get around what is not possible. I also discovered that we cannot begin in the middle, assuming that readers know the basics. When it comes to antenna modeling, modelers come at the enterprise from many different backgrounds, enter it with different interests, and get into modeling loads and transmission lines with different goals and interests. Hence, everybody knows the basics in a slightly different way.

So we shall begin at the beginning--with simple antennas and simple loads-- and work our way to more interesting examples. Along the way, we shall have occasion to mention some useful adjunct calculation programs and some equations for use on calculators. Modeling programs just do not do everything we need to do to make good models. But there are some utility programs that can take most of the drudge work out of modeling.

In the end, we shall quit far short of exhausting the subject, but a little ways beyond exhausting the writer. However, incomplete, I hope the information is useful to you.

Updated 12-29-97. L. B. Cebik, W4RNL. Data may be used for personal purposes, but may not be reproduced for publication in print or any other medium without permission of the author.

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