> My opinion is that radials can only function below the vertical. The
> wave radiated from the vertical must immediately become 511 feet tall
> to propogate efficiently. Since most verticals are less than a full
> wavelength tall, the ground or raidals must act as a reflective
> surface to prevent the wave from digging into the ground and loosing
> power.
The wave does not become a full wavelength tall, and certainly does
not need to become that tall to propagate efficiently.
Visualize the waves from a pebble hitting a pool of water. The period
of the wave has nothing to do with the total frontal area of the wave
as we move out from the point source.
Consider any antenna in freespace receiving a distant signal on
direct wave. We have a wave front geometry that is determined solely
by the distance to the source, it is a geometry problem and not a
wave-period problem. A two-meter signal and a 160 meter signal would
have the same wavefront, just as it would be with a pebble or a rock
in a pond of thick oil or a pond of thin solvent. If it didn't work
that way, collinear antennas beyond 1 wl long would not work.
The real mechanism of loss is due to currents induced or coupled to
the earth. Whenever we intentionally or unintentionally increase
those currents, we increase the power that is lost as heat.
Four radials concentrate the fields around and even below each
radial. The more radials we use, the more area we would spread those
fields over. Each radial would share current, and so the magnetic
induction fields would decrease near each radial. The voltage along
each radial would be reduced (for a given power), and the so electric
fields would be weaker. Losses would be less, as we use more and more
radials.
In order to use a few radials effectively, the radials must be a
large fraction of a wavelength above earth. At 1/4 wl, eight radials
measure to be just the tiniest amount below 100 radials on the earth
surface...for all purposes they are nearly the same. But that is with
the antenna extended up away from earth. There are published measured
FS data for this from an actual BC station system.
If you look at any old antenna handbook, they always warn that a
groundplane antenna must be at least 1/4 wl high or higher above
earth. Based on a few articles that were never verified by actual A-B
measurements of real systems, we now tend to dismiss all the real-
world work over the past century.73, Tom W8JI
W8JI@contesting.com
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