[TowerTalk] Fwd: grounding (again)
steve at nr4m.com
Wed Apr 25 21:36:32 EDT 2018
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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