A direct lightning strike with the voltages to jump from the sky to
ground will ignore small irritations like a dipole center insulator.
I have seen the wire vaporized with nothing (including the center
insulator and most of coax) remaining except an RG-59 coax stump, and
that mostly minus the center conductor. Teenage operator's father's
insistence that the coax be stored outside the window when not
operating, effect of weather on coax & connector notwithstanding,
probably saved a house fire. The path on the ground, where the
vaporized coax was laying, was clearly indicated by a thirty foot long
six inch wide burn mark. Neither tree supporting the 40 meter dipole
was struck. The coax was not grounded in the normal sense, the PL259
was down in the grass. The dipole was up thirty something feet. All
the solder in the PL259 center conductor pin was gone.
Even if the current was flowing on the outside to begin with, the
shield current will induce a nearly equal current on the center
conductor, and both shield and center conductor will present a problem
voltage at the far end without protection steps.
An induced high level voltage will induce to both center conductor and
shield.
If you refer to a "lightning rod effect", if the center conductor does
not connect to a DC, low impedance ground, that half of the dipole
will be without whatever "effect" might be demonstrated on the shield
side.
The above event, while yet a novice operator, and not my own station,
forever informed all my decisions about grounding and the power of
lightning.
73, Guy.
----- Original Message -----
From: "Mark Beckwith" <mark@concertart.com>
To: <towertalk@contesting.com>
Sent: Thursday, December 12, 2002 4:58 AM
Subject: Re: [Towertalk] Lighting Protection and Roof Towers
> >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.
>
> Does this mean that the side of a high dipole which is connected to
the
> center conductor is a target?
>
> Mark, N5OT
>
>
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