[TenTec] OT: Ground Radials at Tower Base

[Jim Brown K9YC]

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