[TowerTalk] K8URs and other vertical arrays with sloping elements

[L. B. Cebik]

All models of vertical arrays with sloping elements--when modeled over a
MININEC ground in order to avoid modeling radials--will show excessive
gain and erroneous front-to-back ratios relative to the same array modeled
over a buried radial system (requiring NEC above -2).  The MININEC ground
has well-established error tendencies whenever any element--driven or
parasitic--has a horizontal component--as do all vertical arrays with
sloping elements.

This is not simply a note based on generalizations, but the result of
extensive modeling in NEC-4 and NEC-2 of vertical arrays in the literature
using the MININEC ground (available in EZNEC only or in MININEC core
programs), barely elevated (0.001 wl height) radial systems, and buried
radial systems.  If buried radials are in use or comtemplated, only a
buried radial model will do (with not all questions of model vs. reality
yet answered).  MININEC ground will inflate gain, deflate source
impedance, and simply falsify the front-to-back ratio for any
sloping-element vertical array, relative to a buried-radial
model.  Vertical arrays with nothing but vertical elements are more immune
to the modeling errors when using simplified ground systems to avoid
modeling radials.

A more detailed study among the vertical array modeling choices will
appear next year in NCJ.

The K8UR system, incidentally, shows excellent promise, but models out as
reducing overhead radiation the most (with no gain reduction) if the
dipoles bend at their centers--for maximum cancellation of overhead
radiation.

-73-

LB, W4RNL

L. B. Cebik, W4RNL         /\  /\     *   /  /    /    Tel: (865) 938-6335
1434 High Mesa Drive      /  \/  \/\     ----/\---    http://www.cebik.com
Knoxville, Tennessee     /\   \   \ \   /  / || /    e-mail: cebik@utk.edu
37938-4443     USA      /  \   \   \ \       ||     e-mail: w4rnl@arrl.org




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