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June 17th 06, 04:41 AM posted to rec.radio.amateur.antenna

wrote:
Thanks Richard and Tom D.

I was worried for a while mythology and the magic dust (not Cheech and
Chong style, but Texas style) would overshadow what really goes on.

Richard Clark wrote:

"few persons realize that when a person stands
in an open field on a clear day, his head has a
potential approximately 300V more positive than his feet
and .... The gradient averages about 180 V/m over land
in the summertime."

We have to be careful with that!

Actually the impedance of the field is very high. When a person stands
in an open field he actually perturbs the electric field very close to
him because his body resistance is very very low compared to the
impedance of the electric field. His feet are not really 300V more
negative than his head unless you would replace everything below his
eyebrows and above his ankles with a very good insulator.

On calm windless days the electric field in the air around a structure
like an antenna is easily bled off even through extremely high values
of resistance, and when the wind picks up, especially when there are
particles of some type, the electric field impedance is effectively
reduced.

There are some people who believe in magic. Some people think a tall
metal structure has a potential difference between ends that builds up
in storms, eventually charging the top of the structure so much it arcs
to the clouds above.

To cure that pure fantasy they put little spikey balls on the top of
their tower, somehow thinking the leakage from that corona that Cecil
knows doesn't exist bleeds off the charge and makes the clouds above
and earth below the same potential.

It's very strange how those people all argue with each other and argue
against themselves, but then that's what happens when too much magic
dust hits an antenna.

73 Tom

For something that doesn't get much ink in the textbooks, static
electricity can be an awfully important subject. I spent years
trying every half-baked, nuthouse remedy I could get my hands on
to try to get paper through a printing press without having sheets
cling to each other due to static attraction. Nothing actually
worked very well. There were plenty of people willing to sell me
remedies, though. I'm surprised no one is marketing a corona killer
for antennas.
73,
Tom Donaly, KA6RUH

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