NEC 4 can be easily used in a few hours with some reading. To
really understand the program would probably require
the equivalent a 3rd year university semester. The program can,
however model an infinite number of antenna designs.

Inputting data is relatively trivial. NEC 4.1 is free, but does
require
the purchase of a license from the Lawrence Livermore
National Laboratory. The cost of a license for non-commercial
use is $500.00, and is available to those living outside the USA.
For US residents the license is $300.

For much easier data entry, and error checking etc., GNEC, from
Nittany Scientific makes life a lot simpler -- cost $795.

Frank
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Thank you very much Frank.
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Reg, G4FGQ