Oh, if we only could.
As several have mentioned, we can only try for a true SPG, but with the
power, cable, and phone coming in from the front and everything else for
the station coming in from the back, there can easily be 20 to 30 feet
or more between these grounds. They are supposed to be tied together
and should with a substantial conductor, or strap. But with the rise and
fall times of the average strike The voltages between the ends of that
30 feet can be substantial.. Actually, my station provides a far better
safety ground that the ones provided at the entrance which are 3 little
ground rods about 5/16ths to 3/8ths inch in diameter and maybe 6 feet
long in a more or less triangular pattern. Within a year after "they"
installed them, the clamps could be easily lifted off the rods
However, as far as I can see, this arrangement "helps" to keep the
ground and voltages closer to the same values. 30 feet can provide a
substantial voltage difference at 1 MHz. The safety ground (earth) in
the station as well as wiring protection appear to help with induced
voltage as well. Induced voltages from a close tower strike appear to
be more in phase with ground (earth) voltages, than more distant strike,
being a reason (right or wrong) that I prefer the tower close. Many
direct strikes never appeared to affect the network, but one >100 yards
fried the network as well as considerable hardware.
NOTE: On Google Earth, look for the intersection of US 10 and 115. The
station was about 5 Mi W of that intersection on the N side of US 10.
The farthest I've had a tower was about 100 yards (300 feet) or 275
meters. (5mi W of Farwell MI) The base of that tower was about 100 feet
above the house roof. I use 3/4" 75 ohm hard line buried in the dry,
sandy soil. I made no effort to connect that tower ground to the house
ground. Although the jacket of the 3/4 in hard line probably served the
same purpose. This was the Western edge of the Saginaw Valley where the
ground elevation came up 400 to 600 feet in only 2 or 3 miles. Coming
from Saginaw Bay they were the first hills of any note in about 80 miles.
73
Roger (K8RI)
On 1/13/2016 Wednesday 3:16 PM, Gary Huber wrote:
Bonding everything (all grounds) to the main A.C. grounding electrode
in accordance with the National Electrical Code avoids voltage
differential during strike events. (at least that seems to be my
experience with commercial repeater installations with antennas at 197
feet or higher)
---
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