Message-ID: <002201c0fa23$de3e5440$87e086d4@ericadodd>
From: "g3ldo" <g3ldo@ukonline.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <R8J+qAABTvL7MwNR@telemetry.demon.co.uk> <000f01c0f8a6$b6efc3c0$f57674d5@w8k3f0>
Subject: LF: Re: Protection against lightning
Date: Thu, 21 Jun 2001 08:24:03 +0100
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>


Dick Rollema said:

> When not in the shack I leave the aerial floating in the hope that it will
> be charged to the voltage potential of its surrounding so that lightning
> won't  "see" it.
> Or is that a misconception?

In a discussion with Arnie, CO2KK, regarding this subject he said that in
areas of tropical storms antennas were best ungrounded and all equipment
disconnected from the antenna, ac supplies and even from ground. However
there should be provision for flashover to ground (at some distance from the
shack if possible) if the antenna static potential becomes excessive. An
ungrounded antenna reduces the potential gradient in the area above the
antenna.

In Kenya I used a rhombic which used to collect static that flashed over to
the metal window frame if there was a wind (and sometimes rain). If there
was a thunderstorm in the vicinity I used to disconnect the feeders from the
ATU and throw them out onto the ground outside.

My 60ft mast in Sierra Leone was hit by lightning one night - it seemed that
the room was filled with a blinding blue flash accompanied by a loud crack.
All the lights went out. I went into the pantry (to check the electrical
fuse boxes etc ) and all that I could see were wires sticking out of the
wall and bits of bakelite and annealed copper on the floor. All electrical
equipment not connected to the ac supply, including the radio, survived.
The ac supply was fed to the house via overhead wires that probably made the
situation worse.

At this QTH the mast is folded over most of the time so the same sort of
situation does not arise. Although the above experience had made me rather
paranoid about lightning I try to tell myself that the chances of a normal
QTH with a TV antenna being hit (in the UK) has been estimated to be once
every 400 years.

Regards,
Peter, G3LDO

e-mail <g3ldo@ukonline.co.uk>

Web <http://web.ukonline.co.uk/g3ldo>