[TenTec] OT: Ground Radials at Tower Base

[Ron Zond]

Hi

I worked at a college FM station where the idea was that a simple rod in the
ground
would be the only grounding. First storm, and the remote was taken out. With
much
effort, the chief tech convinced the higer ups that a radial system made up
of 8
80 foot 0000 copper cables would work as most lightning strikes from the
ground
up. The system was installed, and lightning bolts smacked the tower with
glee.
The transmitter stayed on the air, The system is still working 30 years
later.

Ron
K3MIY


-----Original Message-----
From: tentec-bounces at contesting.com
[mailto:tentec-bounces at contesting.com]On Behalf Of Jim Brown K9YC
Sent: Sunday, August 17, 2008 4:15 PM
To: Ten Tec Contesting
Subject: Re: [TenTec] OT: Ground Radials at Tower Base


On Sun, 17 Aug 2008 13:07:29 -0500, Mike Gorniak wrote:

>Obviously, the radials are critical to the performance of the antenna.
>But it's the ground rods that protect the station from lightning damage.

Hi Mike,

Intuitively, the radials provide a capacitive connection to earth, while
the rods are part of a DC connection that includes both resistance and
inductance. As frequency increases, inductance dominates. Since lightning
is a broadband event (that is, DC to many MHz) with most of the energy
concentrated within several octaves centered around 1 MHz, one would expect
that capacitance to be of value WHEN the strike happens.

I'm not a lightning expert, but I'd want to see some science on that
(controlled studies, lots of installations and events analyzed
statistically, with peer review) before I would accept this statement as a
given. (It's entirely possible that this work exists, of course, I just
don't know about it.) The rods may have prevented damage in your situation,
or it could have been coincidence. What I WOULD accept is the DC connection
(the rods) minimizing the slow buildup of a DC charge that might lead to
the event.

73,

Jim Brown K9YC


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