[TowerTalk] RE: Antenna Grounding

[Constantine, Charles]

Subject: RE: [TowerTalk] Grounding antennas?
Date: Mon, 29 Mar 1999 09:29:55 -0800
From: Chuck Constantine <Charles.Constantine@lmco.com>
To: towertalk@contesting.com

> [TowerTalk] Grounding antennas?
>
> Ted Leaf (tleaf@hotmail.com)
> Mon, 29 Mar 1999 02:23:50 PST
>
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>
> Hi Guys,
>
> Just a thought on the previous post of whether to ground or float the
> coax of a wire antenna when not in use.
>
> If you ground, you may be attracting a lighting strike by offering an
> easy path for discharge.
> If you float, the discharge may find a more convenient direct path to
> ground elsewhere.



Reply:  I disagree, Lightning comes down in "Stepped Leaders".  Each Stepped
leader can be on the order of hundereds of feet per step.  As the leader
comes
down it will take the path which has ionized for it.  If your antenna is the
tallest object within several thousand feet then it "might" be a ground
path.

Prior to a lightning strike as the "leader" starts coming down looking
for a path to ground there are tremendous Electric "static" fields being
generated which cause "streamers" which propagate "Upward" from an object
and
make contact with the downward leader thus completing the path and the
upward
stroke.  The grounded antenna prevents the buildup of static and helps avoid
the
upward streamers.  When lightning striks occur nearby there are tremendous
electric fields induced into everything nearby and the ground provides a
safe
path for this energy to discharge.

Theres a false rumor that "Isolating" an object so its not grounded will
prevent
a lightning strike.  Lightning is going to attach to whatever it wants. By
grounding the antenna you not only prevent static buildup from the
"lightning
induced fields" but also can avoid a personnel hazard.  What I mean by this
is a
un-grounded antenna "something where the center conductor is isolated from
DC
ground" can act like a BIG capacitor and store lots of energy just from
local
air currents.  I learned this the hard way with a ground plane antenna I
disconnected and "Floated" prior to a storm.  I accidently came in contact
with
the end of the coax connector and got a severe jolt!  I then had fun later
drawing an arc every couple of seconds from the center conductor to ground!

Bottom line is grounding or isolating an antenna is NOT going to prevent a
Lightning attachment.  Grounding can actually decrease the chance of
attachment
by preventing static buildup which can generate upward streamers and also
provides a preferred path to ground.  No matter what if you take a direct
attachment theres going to be damage.  You can probably kiss your coax
goodbye
as the lightning will probably arc over through the dielectric on its way to
ground and you will have to replace the wire antenna anyway cuz the
instantanious current and the inductance in the wire will cause it to
"Vaporize"
it into oblivian.

73 Chuck Constantine KR6C



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