Jim,
I feel somewhat 'vindicated' by my setup. I have several 190 foot
towers for my M/M station. Each tower is about 450 to 500 feet from the
shack. Under each I dug 6 - 60 foot trenches in a star pattern, 1 foot
deep and in each trench I installed 4 - 8 foot ground rods, 16 feet
apart, then CAD welded # 2 solid copper between the rods and attached to
the galvanized tower with an interface of stainless steel hardware.
Single point ground on the shack end, with the 12 x 24 inch naval brass
entry panel about 6 inches from the service ground, and, of course attached.
I figured it was better to dissipate the lightning strike as much as I
could at the tower end, then let it 'dissipate' in the shack. Very few
problems lightning problems here.
73 de Steve, NR4M
N0AX and I went through the engineering logic for bonding grounds from
distant antennas to a central point when working on his new ARRL book
on Power, Grounding, and Bonding. We've seen two "rules of thumb," 60
ft and 100 ft, as the maximum distance from the premises that should
be bonded. The reason is simple -- lightning is an RF event, with
energy having a decade-wide peak roughly centered at 1 MHz (i.e. 300
kHz - 3 MHz), and at these frequencies, any bonding conductor becomes
a big inductor. It is FAR more important to provide a robust, low
impedance path to earth at those remote points and bond antennas
there. Low Z, for example, could be translated into multiple rods,
spaced 1-2X their length.
In the shack, treat all of the coax and control wires to a proper
single point entry panel, with protectors on everything.
73, Jim K9YC
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