Dave W0FLS wrote:
With the radials being 4.9 meters above ground, do the radials literally
come up to the tower and then travel down the leg to connect to the ground
side of the insulator or do they travel in close to the tower and angle
downward?
From the text of that paper, it appears that the four horizontal radials are
attached to the monopole by insulated supports at 4.9-m elevation points
above the earth, and terminate there. The coax center conductor is bonded
to the tower at that same elevation, and the coax outer conductor attaches
to the common point of the four horizontal radials at that elevation.
There is no need as far as system radiation efficiency for any of the
conductors of this antenna system to have a physical connection to the
earth. Probably this system does have conductive paths provided by a static
drain choke to a "lightning ground" buried in the earth (maybe a few ground
rods), and an arc gap across the base insulator -- but the paper did not
include those details. They would have almost no affect on the radiation
efficiency of this system, in any case.
Does a FS measurement taken at 1 kilometer fully reflect the true angle of
radiation and overall performance of the antenna for purposes of distant
signals?
The relative field (E/Emax) of the vertical plane field pattern radiated by
__all__ monopoles of ~ 1/4-wave in height and less is very close to the
cosine of the elevation angle. The cosine of zero degrees is 1 (unity),
which means that maximum field is radiated toward the horizon. The cosine
of 30 degrees is 0.87, which means that the field at that elevation angle is
87% of the field in the horizontal plane. Etc.
Referencing back to Clarence Beverage's data, this means that the field at 1
km radiated by that system toward a 30-deg elevation angle is 0.87 x 302
mV/m = 263 mV/m (approx).
The relative values of those fields at an infinite distance over a
real-earth ground plane no longer have the relationships they had at 1 km,
but that does not alter the fact that those relationships existed at that 1
km distance, in the first place.
R. Fry
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