[TenTec] More on verticals

Arthur Bernstein n2ka@optonline.net
Tue, 03 Sep 2002 00:06:57 -0400

>From my over 40 years of hamming, I've found vertical antennas to be
effective radiators. There must be a few qualifications here.
First--what do you hope to work with your antenna? Are you a net QSO
person who is satisfied with QSOS up to 500  miles or so? Then you'd be
better off with a low horizontal antenna such as a dipole on bands such
as 40 or 80/75 meters. Are you a Dx'er? Then a horizontally polarized
antenna will be effective if you (theoretically) can get it up 1/2
wavelength (at a bare minimum) on the band of interest. Horizontally
polarized antennas are much more dependant on height above ground for
effective long distance communication due to proximity to near field
ground loss. With vertical antennas, basically a similar condition
applies. A vertical mounted AT ground level better be sitting on a very
low loss ground plane, such as salt water, salt marsh, ground screen
with lots of metal in it AND little in the way of near field objects
that can contribute to additional loss. An alternative to the ground
mounted vertical (called a monopole) would be one with an elevated feed
point. This may be accomplished in two ways. One way is what is commonly
called the ground plane antenna. Elevate  the feed point, say a minimum
of 10 feet, use say 4 quarter wave radials on a single band antenna or 2
for each band on a multi band antenna. Simple, cheap, and they work well
as DX antennas. The other elevated feed point verticals are the ones we
see advertised that do not require ground planes. The reason for this,
is they are really half wave radiators. Picture a half wave dipole stood
up vertically, still being fed in the middle. The feeding is
accomplished with mechanically routing the coax up in the air to a
matching network or feedpoint that has been elevated. This somewhat
eliminates the counterpoise or radial necessity. The fact that there may
be lossy ground below this or any other antenna can be helped by placing
radials in or on the ground below the antenna in use.
As hams we have to learn to improvise, as few of us are blessed with
perfect locations for antenna placement. I've been using a 1/4 wave
INV-L (130 feet long) on 160 meters for some time. Due to space
limitations (my property is approx. 65x100 ft.), my feedpoint is at
ground level. I have little room for 130 ft. radials-though I have a
maybe 2 or 3 bent all over the place. I have around 30 radials of
various lengths and thicknesses, a couple of inches below the ground.
The antenna is about 50 or so feet vertical and the rest slopes down to
some convenient location. Feed with RG-213/U. With this antenna I've
managed to work 131 countries on 160 meters, including VK6, ZS6, etc.
from Long Island, NY that has probably the lowest ground conductivity in
the U.S. (averages 0.5 micro mho.)
For what it's worth!!
Art, N2KA..