It is a Texas hill (10 acres) - not a Colorado mountain I am talking about.
My qth is about 400 feet elevation above Fort Worth (15 miles SE of me).
The rock is solid white limestone from about 18 inches depth or so within
100 feet of the house and antenna in all directions, then falling off to
chunky rock and topsoil that goes down several feet as the elevation falls.
The soil resistivity is typical North Texas / Dallas soil and has high
conductivity. It is a nice radio location with a six degree slope in nearly
all directions for several miles.
Lightning grounds now include two 32 foot #4 solid copper wire radials for
each of the four antenna guy anchors (which are 10 foot 4.5 inch steel pipe
5 1/2 feet deep). The tower is grounded to a ufer ground in the tower base,
then we drilled a 9 foot x 16 inch hole (never came out of the rock) and put
a 8 foot ground rod in it, then put a single 62 foot #4 solid copper wire
radial for the tower. The tower has been hit numerous times since it was
put up 5 years ago with no more damage than radial wires that have been red
hot and discolored.
Now I want to put a complete #4 ground around the house (ground ring) and
tie lightning terminals (points) from the ridge line of the house. The
house is 66 feet wide at the N-S ridge, 100 feet long E-W and 45 feet wide
at the garage N-S ridge. There will be approximately 12 terminals using #
2/0 copper wire coming from the terminals to ground. The roof (6000 sq feet
of galvanized metal) will be grounded at every cable exit from the house to
ground 5 places as will be the wood stove chimney. (Have not calculated the
capacitance of the roof to ground!)
The single point ground system is located just outside the ham shack which
is 30 feet from a 64 foot Rohn 45 Foldover 4 wire guyed tower and 100 foot
from the power company ground. Interesting, the power company used my
ground at the house which consisted of 3 ground rods driven into rock and
about 4 or five feet long connected to each other with #4 solid copper wire.
This will tie to the ground ring with #4 solid copper wire. The phone
company also used my ground. The only utility ground is at the primary pole
where they simply run a #4 wire to the bottom of the pole and fasten it to a
plate nailed to the bottom of the pole. This pole is 100 feet from the
house.
The coaxes are well grounded where they come off the tower through a home
fabricated aluminum clamp that exactly clamps the coax shields and is
sealed. All control lines going up the tower are well clamped through MOV's
in a box at the base of the tower. Coaxes are grounded at the top of the
tower at the antenna relay box. Two HF and One VHF coax lightning protector
will be added at the single point ground (they are just unplugged for now.
Any suggestions on which coax protectors to buy (if cost IS an object).
The remaining part of the puzzle for me has been how good of a ground is
practical with rocky conditions? I need to add about 8 ground mats. I plan
to use 2 foot x 2 foot x .032 copper plates (1024 sq inches contact area)
clamped and silver soldered to the five 2/O copper ground wires from the
terminals on the house and use two more for the single point ground spaced 8
feet apart and 2 more for the tower spaced 8 feet apart.
The ground plates should be considerably more effective than radials as it
takes 120 feet of #4 to get the same contact area with the earth as the 2 ft
x 2 ft copper ground plates.
I am an Electrical Engineer, own and am familiar with the Poly Phaser book
on Lightning Grounds and the QST articles, but do not have any of the
Polyphaser products in my system. I have to have a practical system that is
not overly expensive. I always enjoy the N3RR site, but my whole antenna
system would barely trade for the 3 wire Joslyn power protector and I would
like to find a lower cost way to protect the ac line also!
Any suggestions for completing or improving this grounding project with
better performance and at a lower cost would be sincerely appreciated. Some
possibilities include:
1) using aluminum cable above ground on the house, although the savings are
probably less than $100.
2) using galvanized steel for the ground plates, but hope to simply use
lighter weight copper plates for now.
3) using #6 copper for the house ring (600 feet) instead of #4.
4) using #4 copper instead of # 2/o for the wiring on the house lightning
terminals (points) to ground. After a previous discussion with W8JI, I do
not plan to use any of the fine mesh wire that is sold for this purpose by
lightning arrestor companies, just plain old distribution heavy strand
copper or aluminum 2/0, or solid #4 copper.
5) would like to find an inexpensive source of 6 inch wide copper sheet
without having to buy a new sheet and cut it from that.
I wish I had soil that I could just drive an 8 foot ground rod in every 8
feet, but I don't. I wish that I could spend another $1000 on the lightning
protection, system, but I hope not to have to do that.
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