I would like to thank the numerous hams who responded to my plea for help.
The problem that was causing my SWR to rise with high power was not in
my shack. The tuner, balun, coax and open wire line were all 100%. The
trouble was at the connection of the feedline to the antenna.
The connection was made where stainless steel bolts passed through the
tubing. The bolts heated up rapidly when running over 500w. At first I
thought the connection was poor, but improving it did not help. From the
way it was heating (away from the point of contact of the lugs to the
antenna tubing) I think that it was due to the ferrous material
(stainless steel) of the bolts heating due to eddy currents in the
strong RF field.
I have experienced this phenomenon in amplifiers, but never an antenna!
I will change the method of connecting the line on Sunday and I hope it
will solve the problem.
--
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/
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