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Old November 7th 07, 06:58 AM posted to rec.radio.amateur.antenna
Roy Lewallen Roy Lewallen is offline
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First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default 80m Vertical over lossy soil

Stefan Wolfe wrote:
. . .
A third antenna, not discussed here, would be a real 1/4 W monopole that is
truely connected to earth ground and uses no radial conductive elements.
Here, the monopole functions as a dipole but 1/2 of the radiation pattern
exists as a mathematical image reflecting against true ground (not a good
conductor of electrons like radials, merely a zero voltage reference point).
Although the mathematical image seems to only exist in theory, the observed
physical effects of RF transmission follows the rules of energy conservation
and the antenna transmits real RF that can be measured as if it were a true
vertical dipole antenna. Now you have seen the real evidence that the host
is the true body of Jesus Christ! ...the radials were simply a false
religion. The phantom/true earth side of the dipole in the 1/4W monopole
ground plane similuates a real metal conductor, mathematically and
physically. The only advantage here is that the grounded monopole is 1/2 the
height of the full metal conductor dipole.


Unfortunately the Earth is largely covered with dirt. It's unclear to me
how you "truely connect" to it. Radials provide the lowest loss
"connection", but you seem to know of a better way. Please describe it
for us.

Even if you could make a zero-loss connection to ground (and a large
radial field comes close enough for nearly all practical purposes), that
dirt still doesn't provide the "mathematical image" of a perfect ground
plane. The net effect of the ground's finite conductivity is that the
low angle part of the radiation is absorbed in the dirt, heating the
earthworms and resulting in a radiation pattern that doesn't resemble a
free-space dipole (or monopole over a perfect ground) very closely at
all. These effects can be clearly seen with any modern modeling program
including the free EZNEC demo. Example file Vert1.ez uses a
"MININEC-type" ground which does provide a zero resistance "connection"
to ground, something you can approach but not completely accomplish in
practice. Compare the pattern of this model to the same one with a
perfect ground (superimpose the two on the 2D plot so they're drawn to
the same scale) to see how poor an approximation dirt is to a perfect
image plane.

Interestingly, whereas radials simulate (very inefficiently) a true ground
system, a true ground system simulates that which the radial system cannot
achieve very well, but both attempt to acheive the same end. One is ground,
the other is more like a counterpoise or misplaced antenna element for a
balanced antenna.


I don't understand that at all. But as you pointed out a while back, I'm
a ham with an American Extra Class license, so I know I can't be
expected to understand anything very complicated. (Worse yet, I took the
exam 44 years ago, so 9/10 of what I knew then is obsolete, and I've
forgotten the rest.)

Roy Lewallen, W7EL