On Tue, 8 Jul 2008 22:46:27 -0400, Noid Wilson wrote:
>Looking for a little insight from your experience. I have used many meters
>to measure the final 'network' resistance number for grounding. Clamp
>meters, quad push resistance, triple clips, etc but I am in the midst of
>ensuring that the final install with the tower, vertical, and SE is the
>lowest value obtainable.
First, study the links below, which are a summary of the concept and how to
measure the resistance to earth of a ground electrode system.
http://www.lyncole.com/articles/Ohms_Law_and_Ground_Resistance_Testing_part1.asp
http://www.lyncole.com/articles/Ohms_Law_and_Ground_Resistance_Testing_part2.asp
http://www.lyncole.com/articles/Ohms_Law_and_Ground_Resistance_Testing_part3.asp
Now, let's clarify what the resistance to earth is. It has NOTHING to do with
the performance of an antenna. It is ONLY there for LIGHTNING PROTECTION. Now,
we see that you're in Tampa, so lightning protection is certainly a very big
deal.
Note also that these measurements are ONLY the resistance of the path at or
near
DC (the AEMC clamps work around 1-2 kHz, depending on their vintage). Lightning
is NOT DC, it's an impulse, so 99% of the energy in lightning is centered
around
a very broad peak (a couple of octaves wide) 1 MHz, so the IMPEDANCE to earth
that lightning sees may be very different, AND it includes the inductance of
the
path. None of the methods discussed are capable of measuring these values at
RF.
73,
Jim Brown K9YC
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