Topband: Best angle of radiation ?

[Paul Christensen]

> 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