Kite antenna - watch out!

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From: Glen Leinweber (leinwebe@mcmail.cis.mcmaster.ca)
Date: Mon Dec 12 1994 - 15:10:37 EST


gang,
     Using a kite to launch a long-wire antenna is a risky business, even
on a clear day with no clouds around. The danger arises from the electric
field between the earth and ionosphere. This field is about one hundred
volts per meter (in the vertical direction), and is always present. Any
antenna launched into the clear blue yonder will aquire a charge large
enough to wipe out a final transistor, or a receiver front end.

     So what's the difference between ordinary outdoor antennas and one
attached to a kite? Earth's electric field is easily distorted by objects
attached to ground, like a tree, or mast, or house (your tower doesn't
have a few kilovolts between top and bottom). A kite-bourne antenna
protrudes into wide open spaces, where it very likely gets charged up.
Your earth-bound antenna is attached to a mast or tree or house, where
earth's electric field is greatly reduced.

     Here are some precautions for kite experimenters, or anyone who
uses temporary outdoor antennas:

     -Add a choke coil to the antenna connector between centre pin and
ground. This will leak away any charge that tries to accumulate. I see
that most modern rigs don't provide a D.C. discharge path from antenna
connector to ground - this is dangerous to your equipment.
     -This choke won't save you if you connect a charged antenna to
your rig after you've put it up: either discharge the antenna to ground
or connect the rig to antenna BEFORE putting it up.

     A few years ago I put up a two-meter 1/4 wave antenna on top of my
tower. The coax snaked thru the window had no connector. When it started
snowing, I noticed a snapping sound every twenty seconds or so. The end
of the coax was arcing over from the charge accumulating in the coax
capacitance. That cable was being charged five or ten kilovolts in only
twenty seconds!

     So how about Bob in Newfoundland - did you put any antennas up
during the big blow? Should be good for MANY extra dB gain. (Be patient
for a reply while they restore his power). :-)


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