Lee,
Raw NEC2 will give erroneous answers for any linear element using taped
diameter.
The Leeson equations for calculating substitute elements of a single
diameter do not just change the element diameter to an average figure, but
as well calculate a length. The actual diameter that emerges from the
equations, as well as the length are functions of calculating an
equivalent element impedancehence, there is no easy way to try to
stumble on to the correct substitute values except by going through the
equations.
The equations, which are similar to but possibly not identical to the ones
developed by Beezley for his programs, are inherent in EZNEC and the
substitute elements can be seen on screen with the right command key.
I do not believe that other programs yet incorporate the Leeson equations,
although a NittanyScientific product (due about the first of the year)
will have them on board. Otherwise, one can precaluate the equivalent
elements using the equations in Leeson's book The Physical Design of Yagi
Antennas, from ARRL.
MININEC programs like AO, NEC4WIN, and ELNEC do not require tapered
diameter corrections and hence give accurate results from direct modeling
of the tapered diameter elements. Use pklenty of segments and strive to
keep the segment lengths equal from one element section to the next.
Hope this is useful.
73
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 9747215
1434 High Mesa Drive / \/ \/\ /\ (Hm) (423) 9386335
Knoxville, Tennessee /\ \ \ \ / /  / (FAX)(423) 9743509
379384443 USA / \ \ \ \  cebik@utk.edu
URL: http://web.utk.edu/~cebik/radio.html

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