I live on a former AM BC site, and cannot see any way that you could
put up
4 elevated radials and disconnect the ground system that was in place.
The ground system here is typical installation and it is bonded with 4 inch
copper strap to everything and anything in sight. The tuning networks
in the
antenna huts were built on aluminum panels that are grounded with 4 inch
strap to the radial field, all gear in the transmitter building is
grounded with
4 inch to the radial field ground. So its virtually impossible to
isolate the
gear etc from the ground system, installing 4 elevated radials really
showed
nothing at all unless they dug up the entire radial field and pulled
them out.
My door and window frames, steel roof and every water pipe are connected
to the radial system.
When running 50KW you dont enjoy RF burns.
My field here has 120 - 300 ft plus and 120 - 60 foot radials, Im sure
4 elevated
radials will do very well.
73 Merv K9FD/KH6
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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