SV: [PCR-1000] Polarity & lightning

Mon, 18 Aug 2003 22:14:05 +0200

I agree, just as I wrote earlier, a direct hit will burn out almost
avery kind of man-made protection circuits
in antenna circuits, including the antennas and equipment connected at
the lower end of lead-in cables. The original question, I think, dealed
more with protection from static build up during hailstorms and the like
and bursts from nearby strikes, in the clouds or between cloud and
ground. In theese cases some of the earlier mentioned devices could
offer a good protection, and can be swapped out for a low cost if they
have "done their job" and failed. Disconnecting is always a good thing,
if possible.

Regarding not grounding, I think it=B4s a myth that non grounded masts,
towers and other high structures should be less atractive to lightning.
Even well insulated towers has been known to be hit by lightning. One
example is a happening back in 1970 when an old longwawe transmitter
here in Sweden was effectively "stopped" during a lightning storm. The
antenna arrangement was five towers in a ring of 200m height and a
central tower of 250m (about 750 feet) height. The lightning hit one of
the well insulated guy wires of the central tower. The wire snapped off
and the whole structure started to swing and went to ground.=20
In this case the wires was really well insulated from ground and the
tower by several big ceramic insulators at even distances along the
wires, in reality so called insulated masts and towers always relate as
ground polarity, seen from the clouds when the leader channel build up
prior to the main strike. I think the lightning says just "thanks" for
the little short-cut on its way to ground.

/Folke  SM7HMS=20

-----Ursprungligt meddelande-----
Fr=E5n: [email protected]
[mailto:[email protected]] F=F6r John
Skickat: den 18 augusti 2003 19:17
Till: [email protected]
=C4mne: [PCR-1000] Polarity & lightning

All electricity has polarity, even the static kind.  The polarity of a
lightning charge does determine how you position diodes if that is what
you are doing, but the bottom line is the electricity in a passing cloud
is seeking a ground and it tends to follow the path of least resistance.
If you have a convenient lightning rod (your antenna) encouraging it to
come home it does just that, and ZAP, the deed is done, and usually
vaporizes everything along the way.

If you provide lightning a path to ground, your little coils and diodes
will be an absolute JOKE.  Years ago when I was in the USAF and a
maintenance guy on a 50KW SSB transmitter hooked to a LPS antenna we
took a lightning hit.  We had every protection is place it was possible
to have, but it really didn't matter.  First the lightning blew out a 2
foot long hole in the side of our 6 inch nitrogen filled copper tube
transmission line.  Then it finally grounded in the foot square, 3/4
inch thick aluminum encased final amp.  That box had four ceramic/metal
klystron tubes, each of which weighted several pounds, along with
associated circuitry.  When we finally removed it's cover the only thing
left was a half inch thick red dust coating on that enclosure.

I suspect you might be saver disconnecting your antenna and not
grounding at all but that is just my theory.

John

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