[TowerTalk] Gap Vertical, Verticals in general

[L. B. Cebik]

> 
> The two books I recommend are:
> 
> The Amateur Radio Vertical Antenna Handbook
> 2nd Edition
> Capt. Paul H. Lee, USN (RET), N6PL
> Published 1984 by CQ Publishing, Inc.
> Library of Congress Catalog Card Number: 74-83411
> 
> Vertical Antennas
> William Orr, W6SAI and Stuart Cowan, W2LX
> Published 1986 by Radio Publications, Inc.
> Published 1993 by Radio Amateur Callbook
> Library of Congress Catalog Card Number: 86-061499
> ISBN 0-8230-8710-7

Although both books are cionsidered classics in ham circles, both contain
dated material that has been superceded.  Indeed, both should be
classified as "vertical with ground plane" books, where gp is considered
to be at or below ground level.

Since Les Moxon raised the idea of shortening radials to equalize currents
and with the advent of studies that have appeared in Com Quart and which
will appear in other places, the relationship of the quarter wave vertical
to a dipole has been restudied with some interesting results that are too
diverse to detail in a brief message.

The key thing to remember is that a vertically polarized dipole, whether
full length or with some kind of hat assembly on one or both ends a. does
not need a further ground plane and b. does vary in gain and elevation
angle of maximum radiation with both 1/ height abouve ground and 2/type of
ground as it affects the far field pattern.  Elevated radial verticals,
GAP, R7(000), and Force 12 ZR verticals all fall into this group.

The history of the 1/4 wl vertical (and its cousin, the half-EDZ or 5/8 wl
vertical) began with LF antennas that were not able to be built as
vertical dipoles.  Hence, arose the idea of the "image" antenna,
essentially a convenient calculating device.  However, method-of-moments
calculations do not require this concept (although it is used with a
perfect ground specified), and NEC-4 can even model wires underground
with decent accuracy.  Vertically polarized dipoles and variants close to
ground are subject to ground losses that affect the far field pattern, and
so are gp systems, whether the radials are on or in the ground or
elevated.  The chief advantage of elevated radials is increased efficiency
with fewer radials, as Chrisman has shown.

The upshot is that we shall likely have to set aside a good bit of what we
used to take as standard absolutes about vertically polarized antennas.
For the new "absolutes," we shall likely have to wait for a new classic on
vertical from Devoldere, Chrisman, or Belrose--or someone else.

Incidentally, unless you live in Kansas or similar flatland or on an
island amid salt waves--in other words, if you live in an urban or
suburban area--you will likely be more pleased with the results of almost
any vertical if you get it off the ground by as much as you can
mechanically manage.  Elevation angle is only one of the problems.
Absorption by surrounding objects--both organic and inorganic--is a second
problem, unfortunately one that cannot be easily quantified.  But it is
easily detected by placing the vertical low and high for a comparison.
And if you put one on a roof top and droop your radials, remember that the
radials do contribute to both the radiation and reception pattern of the
antenna.  Radials are only mute when they are symmetrical and at right
angles to the remainder of the antenna--and hence are self-canceling with
respect to radiation.

-73-

LB, W4RNL



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