Given questions about how well NEC-2 with a stepped-diameter correction,
as employed in EZNEC, holds up against NEC-4 direct modeling of
stepped-diameters, I have placed some notes on my website on the subject.
Ultra-briefly, the question turns out not to be so simple. The
correlation between the two is closest when the steps are small and the
lengths of each section are long and when NEC-2 with correction uses fewer
longer segments and when NEC-4 uses equalized segment lengths and well
aligned segments. Correlation difficulties arise with models like those
of K6STI, who has used short, large-diameter center section in some of his
models distributed on disk with the Antenna Compendium, Vol. 4. These
challenge NEC-4 and require much larger models to achieve convergence. On
the other hand, NEC-2 with correction does not self-identify a convergence
point, and hence, settling on the "correct" model is not always easy
without external data or experience in what makes sense for a give design.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://funnelweb.utcc.utk.edu/~cebik/radio.html
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