On Thu, 08 Jun 2006 14:06:27 -0400, Roger D Johnson wrote:
>'m trying
>to keep it relatively simple for Gary until he comes up to speed.
Simplicity is good only if it is CORRECT. Simplicity that is wrong
leads to (or reinforces) the myriad of misconceptions about the purpose
of earth connections. We've all seen posts here and elsewhere from hams
pursuing that perfect earth connection that is going to make their
antenna work better, or that they need a different earth connection for
power and their ham station. Both are wrong.
>It's my understanding that most ground measurement devices use a low
>frequency (100 to 300 Hz).
Yes, that's true -- and some modern test equipment is moving up in
frequency (I've seen stuff in the 1-2 kHz range) to get away from
higher order harmonics of power that pollute the measurement.
>The result measured is not necessarily
>indicative of performance at RF frequencies.
Right. They will be roughly indicative of the resistive component at
the frequency of the test generator, which will certainly vary with
frequency. It's sort of like trying to nail jelly to the wall.
Grounding for power safety is defined in terms that traditional power
engineers measure.
Red Haines said:
>Ground resistance and ground impedance are not nearly as important
>for lightning protection as is preventing differences among the
>several grounds involved and preventing excessive surges on all
>ungrounded connections.
EXACTLY! I agree with everything Red has said. And MOV surge
protectors on branch circuits are a prime cause of differences between
grounds that can cause serious destruction when lightning hits. I
strongly recommend SERIES MODE surge protectors like those manufactured
by SurgeX, because they don't throw the strike onto the ground wiring.
73,
Jim Brown K9YC
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