I always thought, as Jon describes, that the primary objective of lightning
protection was to continuously discharge the atmosphere in the vicinity of the
antenna in order to prevent the build-up of a large enough potential to cause a
sudden, rapid high current discharge across the air gap. I always thought that
was how lightning rods worked. However, there was a lot of discussion on this
subject on the Antennas mailing list some time ago, and someone corrected me on
this description. Apparently, the mechanism is considerably more complex. I
don't remember the details now, but the person who made the corrections had
pretty good credentials. (I'm sorry but I don't remember who that was.)
But this issue raises another question that has troubled me now that I have
moved out into the country. Lightning rods seemed to have fallen out of vogue.
I still see them on older structures, but not on new construction. Does
anyone know why this is the case? I bet some of you guys in the midwest, where
you have world class lightning storms, would know the answer.
Tnx es 73 de Joe
Yeah, it's all about where the potential can build up. Like I said, if you
can make your antenna/tower look as much like ground as possible and prevent
any charge from building up on it, you are less likely to take a strike.
Lightning is going to occur at the point where it is easiest for the charge
cloud in the sky and the charge cloud at some ground point can most easily
break down or ionize the air between them. Keeping your antennas at earth
ground or as close as possible will minimize that chance. So even though,
you were a "higher" object visibly, you were not electrically.
This may not be a 100% correct technical explanation, but it certainly gets
most of the way there.
One purpose of a lightning system is not just to be able to take hits, but
to be able to avoid getting hit all together. To not get hit is the safest
protection.
73,
Jon
NA9D
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