Lightning tends to melt omni type fiberglasss antennas. The only way I know
to protect them is to side mount them on the tower considerably below the
apex (the phased dipoles that are mounted directly to the tower come to
mind). Every 2 mtr repeater in Florida or Texas has the same problems. I
have never considered putting an air terminal on the tower as it seems to
have enough sharp point to corona quite well by itself.
There is certainly no agreement that sharp tipped brushes or air terminals
can do anything to bleed off the charge of the EARTH (the tower is grounded,
isn't it?)to prevent a strike.
I live on a hilltop location and my Rohn 45 tower is struck regularly by
lightning with no damage in the shack. I subscribe to taking all of the
lines loose when not being used. I lost the FET on an old Yaesu Transceiver
once before I got the antenna removed. #4 Ground radials laying on the
ground have carried so much current, they look like they have been heated
with a blowtorch and quenched in water!
My 22 element 2 meter vertical polarized beam was installed at 90 feet and
looked like the Northern Lights when a storm approached.
-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com]On Behalf Of sparks@apk.net
Sent: Thursday, May 30, 2002 11:18 AM
To: towertalk@contesting.com
Subject: [Towertalk] Air Terminal Placement
I intend to put an aluminum air terminal at the top of my 100 foot tower to
help reduce localized charge accumulation and hopefully lower the
possibility of
a direct lightning strike. I have an omni at the top with a fiberglass
radome
that extends 11 feet above the tower. Do I need to get the tip of the air
terminal some distance above tip of the omni before it will do any good? I
guess my concern is that charge accumulation on the fiberglass omni might
provide a conduction path, effectively making my air terminal useless if the
tip
of the terminal is below the tip of the omni.
Any thoughts on positioning air terminals? Thanks - Jeff WB2RUZ
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