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[TowerTalk] Symptoms of antenna interaction?

To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: [TowerTalk] Symptoms of antenna interaction?
From: Al Kozakiewicz <akozak@hourglass.com>
Date: Tue, 23 Mar 2021 19:30:26 +0000
List-post: <mailto:towertalk@contesting.com>
Still have a foot of snow on the ground, so I'm not quite ready to climb yet.

See photos on QRZ page.

I have 3 antennas on a 10' mast sticking a total of 8' out the top of the 
tower. From top to bottom, 2M7, 6M3 and a C3, all equally spaced.  All were 
tuned to resonance on the ground.

Now up in the air, the C3 and 2M7 are fine, but the 6M3 is useless. The SWR is 
about 3:1 and Z=~70 ohms at the minimum for both.

Is this symptomatic of interaction, i.e. feed point characteristics change 
while resonance frequency remains the same? If so, what is a recommended 
solution? The one possibility I haven't checked yet as it requires climbing is 
a bad rotor loop cable.

Al
AB2ZY
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