Hi,

Good answers to the question !

Always walk away a little smarter after reading this group !

73 luke

Roy wrote:

There are two quite distinct sources of ground loss involved with
vertical antennas. You're talking about one, and Yuri is talking about
the other. Makes for a lively discussion, but it's a lot like the blind
men describing the elephant.

One type of loss is caused when it's necessary to connect one conductor
of the feedline to the Earth. Current returning to this feedline
conductor is equal in magnitude to the current flowing into the antenna
from the other conductor, and it creates a simple I^2 * R loss flowing
through the ground. This loss can be minimized by using a system of
ground radials to decrease the loss resistance R near the base of the
antenna, where the current density is highest. Another solution is to
use a vertical antenna with a high feedpoint resistance. Examples are
the half square, bobtail curtain, and half wavelength vertical. These
antennas require very little feedpoint current, and consequently very
little ground current. They can be very efficient with only a very
simple ground system.

But there's another source of loss, encountered after the signal is
radiated. When a vertically polarized signal strikes the ground, a lot
of its energy is lost to heating of the ground. This is particularly
true at low angles of incidence. The end result is severe attenuation of
low angle radiation. Particularly for low angles, this occurs farther
away from the antenna than a reasonable radial system extends. So you're
stuck with this loss, unless you can physically move your antenna to a
swamp or similar high-conductivity environment. Horizontally polarized
waves react differently.

The demo version of EZNEC will show this quite dramatically. If you
choose the MININEC type ground model, it acts like you have a perfect
radial system. That is, the first source of loss I mentioned is zero.
But the second is still there. You can simulate the effect of ground
system loss simply by adding a resistive "load" at the antenna base.
Compare the patterns of a vertical and horizontal, *to the same scale*,
by superimposing them on a 2D plot, using different qualities of ground.
You'll find it quite educational.

Roy Lewallen, W7EL

Yuri Blanarovich wrote:
But aren't there ground independant verticals, like the Half Square or a
Bob-Tail-Curtain?



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Every vertical "needs" the ground for its efficient performance especially at
the low angles. Vertical dipoles and their elevated cousins are still "looking"
out at the ground, farther waway and with a bit less of participation.
Wanna see dramatic display of salt water "ground" performance/contribution?
Take your any verticaly polarized antenna and compare its performace between
ground ground and salt water ground. You would see somewhere between 10 - 15 dB
difference.

Yuri