On 11/27/2012 10:45 PM, Tim Duffy K3LR wrote:
There is significant coupling between 160 meter antennas that are separated by
as much as 500 feet
YES!
and this coupling could be problem for your set up.
But it can also be a good thing if you know what you have and how to
take advantage of it. I have three resonant verticals for 160M, as well
as a tower that is resonant on 160M. Studying them in NEC early this
summer, I've learned how I can drive each of them, one at a time, and
use the others as passive reflectors to get 4-5 dB of gain in several
directions. The patterns that NEC predicts are clearly observable on
the air.
It doesn't take much to couple and change an antenna's pattern. I first
saw this when I had hung a new dipole near an 80M vertical, and that
feedline coupled to the vertical. I choked the feedline and the
coupling went away. N6LF published something quite useful on this topic
several years ago showing that even a fairly short tower that is well
below resonance, even loaded with aluminum on top, can significantly
affect a pattern. I have one such tower that NEC predicts will resonate
around 2.3 MHz, and a bump of a few dB. Taming that (probably by
detuning it) is something else I need to work on. N6LF's piece is on his
website.
73, Jim K9YC
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Topband reflector - topband@contesting.com
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