Re: NEC-LIST: Software to model effect of boom on elements for UHF yagis?

At 1:55 PM -0500 3/21/02, Ed Troy wrote:
> Does anyone know of any software that will accurately model the effect
> of the boom on the length of the elements of a UHF yagi?

I got good results (matching subsequent laboratory measurements) for
feedpoint impedance and resonant frequency using NEC-2 (although
today I'd use NEC-4) to model a 1.6-MHz (lambda = 8 inches) array
with a nearly one-inch-square metal boom. I modeled the boom with a
mesh of wires, IIRC with the unit cell being one-third of an inch,
although I dimly recall further densifying the grid where the
elements were connected to the boom. (There's high current-density
there.) I used the equal-area rule for wire radius; i.e., I set the
grid wire radius equal to the center-to-center wire spacing divided
by (2*pi). More recently I modeled a similar array using patches in
NEC-4, although I don't have laboratory results to validate this one.

-Chuck

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