On 12/20/2020 7:34 PM, Tim Duffy wrote:
With elevated radials - everything is in play and you have bigtime coupling
between the two antenna systems.
Having high CMI chokes at the feedpoints of all elements is needed to keep
the feedlines out of the picture.
You will need to experiment - trying one thing at a time.
I want to reinforce the advice of others in this thread to extensively
model EVERY part of your antenna farm, including unintentional
components like towers, vertical feedlines to high dipoles, and even
smaller conductive objects.
When I worked in a broadcast consulting office as an EE student in the
early '60s, I learned that things like distant water towers could fill
in the nulls of an AM broadcast directional antenna. The most sensitive
part of most directional antenna patterns is not it's peak gain but
their nulls. Peak gain in favored directions varies a dB or two from
interactions, nulls can be affected by 10-15 dB.
73, Jim K9YC
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