[TowerTalk] References for using a grounded tower as a vertical radiator

[Jim Brown]

On 6/23/2023 11:51 AM, john at kk9a.com wrote:
> Other nearby towers or vertical metal structures can severely distort the
> radiation pattern.

Yes. Also "somewhat vertical" wires like the feedlines to wire antennas 
like horizontal dipoles. These things can be modeled if we know 
dimensions, including spatial details. I spent much of a summer about 
ten years ago working out the interactions between a 120 ft tower with 
antennas on top with my 100 ft Tee vertical for 160M; and between the 
Tee and a pair of sloping wire verticals hanging from the tower that I 
feed one at a time against radials.

The tower acts as a reflector for the Tee, yielding a few dB gain to 
VK/ZL (also a corresponding null to Seattle), and as a reflector for the 
sloping wires yielding a few dB in the direction of the slope; the Tee 
acts as a reflector, kicking both patterns north by about 30 degrees, 
yielding a few dB into JA or EU, depending on which I'm feeding. To make 
all this work, I had apply a short at the base of the antennas that 
acted as reflectors, which I did with a combination of feedline length 
ad stubs.

73, Jim K9YC