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TH-3 antenna problems

Subject: TH-3 antenna problems
From: mikemr@microsoft.com (Michael Mraz)
Date: Thu Feb 11 14:00:42 1993
I had a similar problem with my Hy-Gain vertical. I was running 1kW on 80m
when the SWR shot way up and stayed there. The weather was wet, but that
had never been a problem before. I shut down and inspected the antenna. One
of the large piston capacitors (the 40/80 cap) was too hot to touch near the
bottom, which is open to the air. There was a distinct smell of burning
polystyrene also (smelled like when we were kids and torched our plastic
airplane models).

I pulled the capacitor off the antenna and took it in the house. Closer 
revealed that a spider or other critter had made a home in the 
capacitor, between
the inner and outer conductors. The high power had baked the life-form and
caused a carbon track which then arced quite nicely, melting the polystyrene
spacer in the process.

You may have the same problem. I bought an old TH-6 that had a balun that was
defective. When I opened it up, there was a nest of earwigs in it, some 
alive, some
fried. You might start there, because a trap problem should only affect 
certain bands.
Also, older Hy-Gain traps may not have the drain holes drilled in the 
trap caps, and
if water does enter the trap, it is "trapped" there and will take a 
long, long time to
evaporate (this info from Al "Mr. Antenna" Caplan at Hy-Gain).

73    Mike    N6MZ    mikemr@microsoft.com

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