On 7/5/2013 3:44 PM, Pete Smith N4ZR wrote:
Every time Towertalk starts off on one of these threads I feel compelled
to add one skeptic's viewpoint, and this time I'm actually going to do it.
I'm not a EE but I managed to get over in while earning a degree in CS.
I have a 100' 45G that had a 30' mast with a TH5 at 100', a 7L C3i
6-meter Yagi at 115' and a cross boom at 130 feet with a pair of 11L
440s ans a pair of 12L 144 antennas.
http://www.rogerhalstead.com/ham_files/Tower29.htm
When first installed this system took at least 3 direct hits a year for
a total of 17 visually verified hits the first 6 years it was up. The
only loss was one Polyphaser at the entrance.
There is over 600 feet of bare #2 CadWelded to 32 or 33 8' ground rods.
There are two parallel runs from the tower to the grounding panel and
ground rods at the entrance.
http://www.rogerhalstead.com/ham_files/cablebox.htm The photo at the
entrance is out of date as that panel/box has been replaced with a
larger one.
During that time the rigs remained connected to the antennas, power,
computers and network. They stayed connected because the connections
were very difficult to access. I was more concerned about the
connections to the computers and network as they are on a different
circuit along with the cable connection.
BTW the stations in the house and shop are on serrate electrical feeds
although from the same transformer,
Unless you are an electrical engineer with deep understanding of
lightning protection, I think that attempts to replicate a commercial
24/7 always-connected solution are far more likely to fail than to
succeed.
Lightening protection is pretty well standardized and there is plenty of
information available. There is no 100% guaranteed, fail safe
protection even for the 24 X 7 stations, but they are well protected
from most strikes. It's just that there is no guaranteed protection
from the so called, "super strikes" that can be many times more powerful
than your run of the mill, every day strikes.
So, yes, the best protection is to disconnect everything from everything
else, not just the antennas and power. Remember a strike a mile away
can induce as much as a 1000 volts per meter into a piece of wire,
Another danger is precipitation static, What heavy snow in high wind
can induce into an ungrounded quarter wave, 40 meter vertical is
something to behold and I've never seen an ignition coil produce that
kind of voltage.
Twas about 35 years ago. We were in the process of building a house on
the NW corner of the family farm. I had a 40 meter, 1/4 wave vertical
about a 100 feet out. The rig, a Kenwood TS820, was disconnected. A
very strong wind was blowing with heavy snow. I kept hearing a loud
snap or pop! I looked behind the rig and was surprised to see a FAT
blue ARC across the PL259. The thing is, it wasn't just cross the end
but rather arched out a good inch away from the end of the connector,
forming a loop that appeared to be close to a couple of inches long and
it was loud!. Rain with strong wind can also produce similar results.
I've seen similar results from nearby lightening strikes from the
feedline to the 75 meter dipole.
<snip>
73
Roger (K8RI)
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