Hi Gang,
I've read some of the websites and notes you've all suggested with
interest. (This is a subject of great interest to me, since I've just
finished installing my tower!)
Here's what my ground system looks like. I have a ring of 4AWG
copper around the base of the tower, with eight ground rods connected
to it around the circumference. There are also 8 eighty foot radials
fanning out from the tower, cadwelded to the ring, with ground rods
every sixteen feet along each radial. There are forty ground rods in
all.. The tower (a TM-370D Sky Needle) bolts to a steel base which
is attached to a large welded rebar cage suspended in 11 cu yds of
concrete. Two lengths of 3/4 in rebar are welded to the cage and
extend out through the concrete and are attached to the copper
grounding ring. There are also four copper cables clamped to the
mounting feet of the tower which connect to the ring. The rebar cage
is connected to the ground system to provide a low resistance current
path between the rebar and the ground system. Otherwise, I was
concerned that destructive current would flow through the moisture in
the concrete.
One of the eight radials runs undergound to my station, a length of
130 ft. It has a ground rod every 16 feet along its length. At the
station, each of the three operating positions has a heavy copper
ground wire that is terminated at the entrance point to the radial (a
single point ground).. ALso, the rebar in the foundation to the
station is bonded to the entrance point.
The coax from the tower is bonded to the ground system at the tower
base and also as it enters the house, and there are surge arrestors
on each of the control cables.
Lightning in New Mexico is ferocious, must more potent than anything
I've seen in my previous Ohio QTH. Furthermore, the ground
conductivity is quite low, which makes any ground system challenging.
73,
Jim W8ZR
*************************
James C. Garland
102 Spur Ranch Road
Santa Fe, NM 87540
www.w8zr.net
*************************
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