[TowerTalk] Re: Dipole is Zapped !!

[Jim Reid]

Some days ago,  I posted this question:

> What's happened to my EF-140S,  "linear loaded"
> 40 meter dipole?  Now shows very low real part of
> the Z,  and of course,  very high vswr: 5:1 where it
> used to be 1.2:1 around 7035 kHz.  This,  as measured
> down below at the input to the feedline,  50 ohm coax.

Not sure yet exactly why the above has occurred,  but
much of the time the dipole is now operating correctly!
I did lower the antenna "crank up" support,  and tried
to reach the small matching coil below the dipole.  But
it was just out of reach,  and I became fearful for
my bones while standing on the roof and trying to
direct a 15 foot long pole straight up to poke at the
coil,  hi;  seemed I got a bit dizzy,  and did not want to
lose balance on the pitch roof!  So gave up.

However,  I looked the antenna dipole over using binoculars
for a good view.  Saw nothing out of sorts,  EXCEPT,
the small u-clamps that clamp the aluminum (I think)
linear loading wires in place,  are very badly encrusted
with rust.  Obviously these u's are not stainless steel,
and have only been out in the elements here about 1
year.  I suspect now that my occasional high vswr 
could possibly occur as a result of rust build up actually
opening up a contact between the linear load wires and
the "jumper" connector the bridges across the inner and
outer tip element "fold back"  loading wires.  Or perhaps
the heavy rust build up is causing some other sort
of mischief.  Seems to be showing up only when
the trades are about;  we have had a period of
light to no wind,  and the dipole was operating fine,
but yesterday the trades were back a bit,  and had
a "happening"  occur again while running about
200 watts to the dipole.  And light winds are certainly
enough to cause the long elements of the EF-140 to
wave about and induce motion between the linear
loading wires and the stiff jumper wires.

All of this is just a guess.  I am going to try running
a full 1.5 kW to the dipole to see if this might
"burn through"  such a rust path or some other
possible corrosion.  Too bad for this to have
occurred here in a tropical climate.  Guess I
should have sprayed the antenna down with
clear Krylon or, maybe better, cold galvanizing paint.

Maybe we should all switch to stainless u-bolt clamps
used for various purposes on linear loading wires.

73,  Jim,  KH7M


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