Most of the reasoning for this unexpected negative result was attributed
to the minor high-angle lobe produced by the 5/8 wave coming back down and
interfering with the main lower angle signal. As a result, those station
who had experimented with 5/8 wave towers usually reduced them to 1/2 wave
or less.
From a historical perspective, the 5/8-wave vertical radiator was conceived
by Stuart Ballentine in 1924 and is documented in the Dec., 1924 issue of
the IRE Proceedings. Between 1921 and about 1930, Marconi-fed caged-T,
inv-L, and Fan arrangements were used and required multiple end supports.
These arrangements had carried over from the antennas used in 2-way spark
communication.
Use of Ballentine's 5/8-wave radiator first appeared around 1930, but it was
then quickly realized that a high-angle lobe returning from the ionosphere
destructively added to the ground wave and caused severe fading, typically a
few hundred miles from the transmitter. Shortly after 1930, antenna height
optimization occurred roughly around the time of the BL&E study. So, the
final result of the optimized 190-195 electrical degree monopole radiator
occurred nearly simultaneously with the use of BL&E's systematic radial
development. The destructive effect of the high-angle lobe is more
noticeable with high-power stations. Stations with low to medium power
rarely bothered with anti-fading antennas like the 190-195 degree radiator
and the Franklin design.
From about 1934 and forward, typical tower heights of 60-195 became common
and that's what we still see today. As we know, without top-loading
radiators less than about 60 degrees begin to show diminished field
strength, but at heights between 60-90 degrees, there's little variation in
field strength with a standard broadcast ground system.
Paul, W9AC
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Topband reflector - topband@contesting.com
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