OK...here it goes....
Some of you brighter lads on the I-net can elludicate me on the issue of
grounding the tower. I understand that a tower should have a good ground
and that connecting the tower to the ground is critical. Most people use
heavy gauge wire and a bunch of hose clamps.
My question is this...Isn't a grounding system to "blled-off" the voltage
differential? In other words, should a good ground provide a good path
btween the earth and the sky so no discharge EVER takes place?
I that is true, then theoretically the tower should never be hit by
lightening, or have a discharge event.
Now in practice that isn't the case. For example, I was a broadcast
engineer for a small FM radio station that got hit numerous times during the
year. The whole thing was tracked down to a veru crummy ground that was 20
years old. Also, the ground was based in rocky limestone ground on top of a
hill. The hill is a limestone hill in Northeast Kansas. Everything on that
hill was being hit...from the tower, the guys, trees and Kansas sunflowers
stading a little too tall. A Hustler G7 was blown off the tower and all
electical outlets were blown out of the shack. No electronic devices were
harmed. except the repeater controller which took an EMP hit through the
phone line.
To solve the problem, we had to dig down 15 feet with a backhoe where we
place a 10 foot ground rod in the ground using a portable air hammer mounted
on a truck. A heavy copy cable was the clamped and silver-soldered to the
ground rod and then clamped and silver-soldered to the tower. We did this
to the east and west of the tower. All coax was grounded to the tower
before going into the shack. Also, the coax was grounded to the tower at
the top, middle and bottom of the tower. We also trenched in a #4 wire from
the electrical entry box to the power pole where the polepig was mounted.
The ground was so bad that the return legs had a votage drop between the
pole pig and the load. Then we also bonded all equipment and equipment
racks to the tower ground.
This stopped the massive lighting strikes. Nothing hits the hill anymore.
To me the concept is that the charge is being bled off before there is
enough potential difference to cause a discharge. Same theory works for a
smaller 60 foot tower.
If I am wrong with my physics...then let me know. I guess that to get a
perfect ground that .1 ohm is needed through the whole system.
Just a thought to kick around....
Lee
k0wa@southwind.net
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