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[TowerTalk] Help with a 4 sq antenna problem

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Subject: [TowerTalk] Help with a 4 sq antenna problem
From: "Alan Scher" <WD8PKF@awcmail.com>
Date: Thu, 26 Nov 2009 09:45:33 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hello Tower Talk 
I have recently put up a 4 square 160mtr antenna system. I have a 200 ft rohn 
tower, and have suspended 4 1/4 wave wire antennas using a comtek hybrid 
controller. The vertical wires are bottom fed, and I have put out abt 5,000 
feet in radials on the ground. The array is fed with 500 feet of LMR 400 
coax.The antenna is in a back pasture with no other antennas or towers close 
by. The tower is dedicated to the 160 array.The problem comes with 
transmitting. At low power 200 watts or lower all appears to be fine with 
almost no dumped power, but with the amp on there is a sudden jump in swr to 
2:1 with some pwr loss <10%. Once th swr is up it remains up even with low 
power. After a period of time the swr will drop on low power to flat once 
again. The problem is somewhat intermittent and is more noticeable when it is 
raining or has rained. but it has happened in dry wx also. I have put an new 
ACB 160 in line and the same thing has happened. The feed coax on a dummy load 
is flat. All
  connectors are tight and waterproofed and I have good solid grounds at each 
antenna. When the problem is not present the antenna plays very well, but when 
the swr is up the efficiency is greatly down. Can anyone give me some idea 
where to start with this problem and some ideas on a fix before the snows come?
Thank you for any help
Alan   WD8PKF
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