On 6/23/2023 11:51 AM, john@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
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