Agree that RF design is the key AND low resistance is good. Of course
there are exceptions, but perhaps not common among ham installations. I
climbed several mountains in ME, noting the lightning "ground" on the
top of one with a mostly bare granite summit. There were no ground rods
I could find, but there were a lot of cables in a mesh configuration
over a half acre or so of granite. I doubt there was a DC ground
resistance anywhere near to ten ohms. The mesh was the best they could
do for lightning strike dissipation. Probably would have a great corona
show in a strike, but who would want to be there to see it?
Google earth shows a new tower on that summit, Boundary Bald Mt, ME. It
would be interesting to know the grounding system design. What is there
had to arrive by helicopter. One group climb I did on that summit had
some folks arrive by JetRanger so I know there is a flat enough spot to
very carefully land a 206.
Grant KZ1W
On 1/10/2016 10:48 AM, Jim Brown wrote:
On Sun,1/10/2016 10:26 AM, Grant Saviers wrote:
"The resistance of the grounding electrode system is only a general
measure of
merit. Proper design and installation of the grounding electrode
system, installation of ground rings, ground rods, radial grounding
conductors, and the bonding of systems and equipment, is as important
as the resistance to earth."
This the most relevant statement in the several you have quoted. Think
about it -- many (most?) VHF/UHF communications facilities are located
on mountaintops, where the "soil" is largely rocky/sandy. Heroic
efforts are required to attain even a modestly low resistance to earth.
At the height of the telecom bust, a colleague bought two
decommissioned AT&T Long Lines sites on mountaintops, and I had a
station in one of them for a while. I had the opportunity to study
AT&T's drawings for the building and for the grounding. Every detail
was noted; there are many earth electrodes, and there is extensive
bonding both inside and outside the building. This particular site is
on a 3,000 ft peak in NorCal, with a 2-story building that is 120 ft x
60 ft and a 150 ft tower that is 32 ft x 32 ft at the base and 24 ft
square at the top. There's a photo on the W6BX qrz.com page, which I
shot from a wooden fire observation tower about one hundred feet
higher at the actual peak.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|