Interesting page on the subject here ;
https://ham.stackexchange.com/questions/3675/what-is-the-effect-of-using-different-number-of-radials-with-ground-plane-antenn
On 23/3/21 1:55 pm, Guy Olinger K2AV wrote:
A counterpoise is what we do when the full size of a double-ended
antenna, dipole, OCF, etc is too large for us to build, maintain, etc.
Very simply, we want to jam the energy from the shield of our coax
into the counterpoise, and the energy from the center conductor into
the radiating element, the vertical, T, inverted L, etc, the aerial
wire. Then we want to get all that energy back from the counterpoise,
none lost if possible, at the phase reversal. Any you don't get back
is mostly outright loss. With commercial high grade radials you can
show that the effective series resistance of the counterpoise is 1/2,
1/3 or sometimes even 1/10 of an ohm. That means that the aerial wire
is radiating something like 50, 100 times the energy lost/radiated by
the radials' connection to ground.
The two current destinations taken together MIMIC a circuit, because
the current into the counterpoise is the same, but opposite polarity
as the current into the radiating part of the antenna. If the currents
are equal and opposite, it looks like a circuit, walks like a circuit,
quacks like a circuit. You can model it with a fake circuit, and use
Maxwell's equations for circuits to predict what is gonna happen.
There is no magic circulation, just the ability to convince the coax
it is hooked up to a circuit. With the massive parallelism of a
commercial grade radial field, the radial's electrons are coupled into
the ground as a reservoir, with the push back from extra or missing
electrons that will return the current when the phase reverses. The
more radials, the more even the radials, the longer the radials, the
lower the power lost to current through resistive materials, lost to
dielectric loss in dielectric materials, lost to resistance in the
wire. Not perfect return, but a nice, high percentage return.
In free space, it is possible to construct a counterpoise that NEC4
can accurately predict will radiate power to the far field at a rate
30 dB below the RF current's energy. The essential loss is in the RF
resistance of the wire. You are talking about a counterpoise that is
98 or 99+ percent efficient in free space.
We are not interested in a counterpoise radiating, or invoking loss in
the environment. Talking to the counterpoise, I'm telling it I'm
giving it this pile of energy. A half cycle from now I want it all
back. No skimming off the top. Maybe just a skoch.
A commercial quality radial field beneath a vertical is deliberately
intended to be non-radiating. Looking at the current around the base
of the vertical, the current to the east is exactly the opposite of
the current to the west, as are to the north and south, as are all
opposite radial pairs, therefore the fields generated are opposite,
intended to be net zero in the far field. That's on purpose, pretty
much true, and exactly what the engineers had in mind.
It is easy to show that there are unfortunate ham designs and
implementations of the counterpoise/aerial concept where not even 10
percent of the power is radiated skyward. That is the 160 meter two
ton elephant in the room that gets ignored an awful lot of the time.
73, Guy K2AV
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