An anecdote:
Yesterday several of us were working at my (borrowed)
commercial tower putting up my new 160m antenna. The
tower owner has a VHF 10C4 at the very top of the
tower (325') fed with Heliax. As the brave, strong
tower climbing guy went up he cut the tie-wraps round
some of the coaxes going up the tower. Suddenly the
commercial radio in the hut started relaying the local
AM broadcast station, which is only about 2km away and
has a field strength which can undoubtedly be measured
in volts. Panic!
To cut a long story short we found that grounding the
coax outer where it entered the duplexer cured the
problem. Further investigation showed that the only
ground on the feedline was through the radio/power
ground, EXCEPT that the Heliax/RG213 transition point
connectors just happened to touch a grounded conduit.
Our moving the coax had slightly dislodged it. A
tie-wrap 'cured' it.
This is a commercial installation. NO ground on the
coax at the base of the tower. NO lightning surge
suppression whatsoever. The system has worked entirely
due to God's good graces.
I'm not quite sure what to do here. I could obviously
put a proper coax ground and lightning suppressor at
the base of the tower. But then I'm interfering with a
commercial installation. If I do nothing, the fault
will probably reappear at some point. The tower owner
is completely non-technical and I fear if I mention it
to him he will assume it is because of my equipment.
Thoughts anyone?
73 Roger
VE3ZI
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