[TowerTalk] Vertical Monopole Modeling Problem

[Malcolm Clark]

While playing with the evaluation copy of NEC4WIN95 I attempted to model
a 40 meter vertical monopole consisting of 35 feet of Rohn 25G with a
drop wire two foot off the tower.  The result showed a source impedance
way out of line with what I *think* it should be.  Varying the stand-off
distance changed the impedance but did not bring it anywhere near what I
expected.  On reading NEC4WIN95's help file I found a reference to ratio
of wire diameters that seems to say that the software likes ratios of
5:1 of less and can't handle anything exceeding 10:1.  Even with a drop
"wire" made of 1/2 inch copper tubing, the ratio far exceeds ten.

Unfortunately, NEC4WIN95 doesn't seem to come with a manual, even on
disk (you'd think for the sixty bucks Orion wants they could provide a
manual), so I can't tell if there is any work-around to this ratio
problem.

Anyone out there have any experience modeling tower based vertical
monopoles with this or any other software?  Your comments would be most
welcome.

Thanks.

73 Malcolm KR4HP

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