Don't forget that there is a big difference between:
1) electrical safety ground (the green wire)
2) Lightning protection ground
3) RF common
Single point ground is fine "within a box", but you start running wires out
of the box and you need to carefully contemplate what's going on.
The green wire ground can be RF high impedance...it's designed to conduct
60Hz....
The RF common (i.e. the coax shield) can (and should) be isolated from a
conductor designed to carry lightning currents. Some recommendations I've
seen are to run the coax through an isolated (i.e. not buried) piece of
steel pipe, which acts as a nice choke for fast transients.
There's also NEC requirements for the physical grounds to be interconnected.
Jim, W6RMK
So, to your question:
At 05:18 AM 8/9/2003 -0700, John Dooley wrote:
>At the Polyphaser web site Engineering notes:
>"The tower ground system and the single point ground system must be
>interconnected. This interconnection should be below grade and with a bare
>low inductance conductor. The coax cable shield must not be the only
>interconnection between ground systems." My question is Does this imply I
>run a ground lead directly from my grounding grid at the tower 120 ft. to
>the entrance panel and connect that with my electrical single point
>ground, then additional ground connection to the ground rod located at the
>back of my equipment? Very confused and can't seem to know if I will
>create a loop where all potentials will not rise and fall at the same time
>if I have a direct hit. Right now I'm installing my US Tower TMM-433
>approximately 120 feet from the garage entrance and see a need to create
>an entrance panel for the 1/2 hard line feeding the antenna at the tower.
>I plan to ground the hard line at the top of the first tower section and
>at the base, this will be tied to three ground rods around the outside of
>the tower form all interconnected by cadweld one shots. But does the
>technical article call for an additional ground line run over 100' to my
>entrance panel also. The plan is to ground the entrance panel to a ground
>rod at the feed line entrance to the shack and have this tied to the
>electrical single point grounding grid in the home. Somewhere I feel I'm
>missing the validity of having a "single point ground" because of all the
>measures I'm planning on taking, or just not experienced with a solid
>reliable system that I can draw designs from. Can anyone help me with this???
>Thanks,
>John W6ZIP
>Victorville, Ca.
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>any questions and ask for Sherman, W2FLA.
>
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