K9YC wrote:
The problem with this (and any) analysis of a lightning event is that it is FAR more
>complicated than anything we can compute, simply because the voltages and currents
induced >in any system (stuff wired together) will be different in each conductor
depending on >WHERE the strike is, the physical geometry of the conductors that make up
that system, how >energy from the strike gets to the earth, etc.
I can attest to that ! In 13 years of living on a dry, New Mexico
hilltop, I have learned a lot about mitigating lightning damage.
Frankly, the cost and effort of doing lightning protection "perfectly
right" is prohibitive. The approach I have settled on is simple
disconnection to keep the bulk of the lightning energy out of the house.
All RF and control cables to/from the towers (I have 3 towers, with 5
rotator controls and a number of remote antenna switches) terminate on a
bulkhead panel about 30 feet from the house. During lightning season
(May-October), everything is disconnected at the panel, except when I am
on-the-air. All AC power to the ham shack is disconnected, except when I
am on-the-air (unplugged - I don't trust the small air gap in switches
and relays). Yes, this makes it inconvenient to be on-the-air during the
summer. Even with these measures, I have learned the hard way about
interconnectedness (K9YC's "stuff wired together"). A nearby or direct
hit to a tower will destroy USB ports on computers and radios, if they
are interconnected with a USB cable. I have tried commercial USB
optoisolators, but have found they generate too much RF noise. The
latest incident was earlier this week. I had a direct hit. The only
"stuff wired together" was an Astron power supply, connected to a 2
meter radio. Just before the storm, these were working fine. I unplugged
the antenna from the 2 meter radio, and the AC power from the power
supply. There was still a 3' long power cable connecting the power
supply and 2 meter radio. After the storm, the power supply blew fuses.
The root cause was a fried LM723 in the power supply, causing the
voltage to go high, and the crowbar protection to be activated.
Sometimes I think moving to relatively lightning-free coastal Oregon
would be a good idea !
73,
Steve, N2IC
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