LB mentioned inefficiency of elevated radials is related to the
"unbalance" of current in radials. I disagree with that one statement.
Radiation is not a major source of system loss, no matter what a current
meter indicates, unless the radials are a long distance above earth or
unless a greatly non-symmetrical elevated radial system is used.
1.) Cancellation of radiation and induction fields is a distance related
problem. No matter how well current is "balanced" in radials, radials
couple to via radiation anything between zero and several radial lengths
away in some directions. They also couple to anything within a large
fraction of a wavelength away by induction fields, even if current is
perfectly balanced.
Assume we have a pair of 1/4 wl long radials on 160 meters, 120 feet long.
If current is perfectly balanced, radiation and induction fields only
cancel more than a wavelength or so from the two radials in most
directions! That's several hundred feet.
Distance to the far point has to be essentially equal to all area with
equal and opposite charges and charge movements, otherwise coupling occurs.
For example? Assume we are 1/2 way out on one radial at ground level, and
the radial is ten feet high. We are only TEN FEET from one area of one
radial, and 120 feet from the area carrying equal and opposing currents!
No way does radiation cancel at all, nor do induction fields cancel. That
radial drives the earth below it almost like the other radial does not
exist, except the other radial reduces the driving current by half. Losses
would be (considering only current) reduced only six dB by the second
radial over just a single radial. Of course that is an less than ideal
analysis that considers only current.
With 60 radials, current density would be 1/60th value using a single
radial. Losses are reduced by the square of the current density, or 3600
times (reduced almost 35 dB).
The above is oversimplified, but it still illustrates the great power loss
difference possible when current is spread out instead of being
concentrated in one area of a lossy media.
In other directions, with only a few radials, radiation NEVER completely
cancels no matter what the distance. That's why a 1/4 groundplane with four
perfectly spaced and equal current radials has a distorted pattern. Of
course the effect is worse when the antenna is jammed down against earth,
and that's why ALL the knowledgeable books always cautioned a ground plane
antenna needed to be at least 1/2 wl above earth. Those old guys had to use
meters, because they didn't have computers!
The key to remember is distance. The distance from the point of interest to
areas of the conductors (radials) carrying equal and opposite charges or
charge movements has to be exactly the same in order for complete
cancellation to occur.
The coupling to earth is essentially the same whether currents are balanced
or not, although earth losses might be reduced IF the earth below and
around the wires is homogeneous and there are no other conductors coupling
to radials. I doubt anyone has that situation.
2.) If the earth below or anywhere near the radials is NOT homogeneous, and
if there are other conductors around the radials, minimum far-field will
occur when the radials are intentionally unbalanced.
If the environment is not perfect, re-radiation from the radial's
surroundings will NOT be equal. Balanced current will guarantee far-field
radiation in this condition, which I suspect is an extremely common
situation.
As a matter of fact the tendency of radials is they have the LEAST current
in the least effective radials. Current actually moves into the "more
effective" radials all on its own. Forcing current to be equal can actually
move current into the areas of greatest loss, and accomplish exactly the
opposite of what has been theorized, since the bulk of losses are near
field losses and are NOT affected by far-field cancellation of radiation.
3.) There is absolutely nothing that indicates lack of efficiency is do to
anything more than not enough radials, which simply means current density
in the lossy soil below the radials is concentrated in a smaller area.
Concentrated current (and electric fields) always increases loss for a
given media surrounding the antenna.
I'd like to remind everyone again, that NONE of the recent counterpoise
articles have supporting field strength data of actual A-B tests on one
system...not even a crude test. Without supporting data, this stuff is all
just a personal opinion of what might really be happening.
Because of the complexities involved in near field losses, even if one
system works (and even if it does NOT work) no one can say the same applies
to other systems. This is especially true in a small area with all kinds of
other conductors around the antenna.
My measurements don't prove elevated systems never work. They simply prove
they didn't work for me (and for a few other cases) no matter how carefully
they are installed. This was true in an open pasture with nothing else
around for a wavelength or more, and in two rocky soil environments.
The only thing we know for sure is that when a large number of radials are
used, the system becomes non-critical and virtually always works at the
maximum efficiency possible for a given location. With only sixty radials
1/4 wl long, it has been proven time and time again efficiency approaches
100%. That we know.
The rest is all guesswork. Unfortunately the guesswork disagrees with
physics that works perfectly for everything else in the world.
73 Tom
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