[TowerTalk] Fwd: grounding (again)
jim at audiosystemsgroup.com
Wed Apr 25 19:08:53 EDT 2018
On 4/25/2018 11:06 AM, Bob Shohet, KQ2M wrote:
> I am now contemplating grounding the Comtek control boxes of both 4-squares to an 8’ ground rod where they are.
> I am also still contemplating running an AWG 4 solid bare copper ground wire between the towers and using ground rods to ground it along the way.
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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