[TowerTalk] Ground Resistance

[Jim Brown]

On Tue, 8 Aug 2006 22:25:38 -0000, David Robbins K1TTT wrote:

>simple, not really.  There are meters made for measuring ground
>system resistance,

Yes. These testers are attempting to measure the resistance of the 
path to "earth" at frequencies near DC. This may be repeatable, 
but it is of limited value for quantifying the effectiveness of a 
ground for discharge of lightning (which is the only good reason 
for going to earth in the first place). That's because the energy 
in lightning is broadly centered around 1 MHz, with lots of energy 
a couple of octaves above and below that. It should come as no 
surprise that the connection to earth is quite frequency-
sensitive. 

Note that this measurement tells us next to nothing about the 
behavior of the ground connection as part of an antenna system 
(and it isn't very useful as part of an antenna system). 

I saw a very nice PPT online of a presentation on ground radial 
systems that was done at Dayton a year or two ago, I think by 
K3LR, but maybe someone else. He was addressing the effectiveness 
of a radial system as part of an antenna (essentially, a 
counterpoise), and comparing what happens at 7 MHz, for example, 
to what happens on the AM broadcast band (for which we have lots 
of excellent data). 

73,

Jim Brown K9YC