Topband: Have a pproblem with my 4 square on 160 mtrs

[Alan Scher]

Hello Topbanders,
 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