Am Donnerstag, 14. Mai 2009 schrieb Rob Fugina: > > Ok, you're right, and I'm not really trying to protect myself from a > direct strike. But having a 75m antenna sticking out into my back > yard > 75m band, I think? If it is really 75m high, someone should already have done deep thinking about lightning...
> does seem to be asking for nearby lightning, or overhead
> lightning, to induce significant current in that wire -- or am I
> wrong?
>
No, you are pretty right. But it's just the way a direct lightning strike will
damage any electronic equiment in a range of ~50m, regardless of protective
circuits. It just runs over any surface and grasps any kind of conductor.
Optocouplers are no match for lightning -- it just made it about 2kms down to
earth, so 2mm would be no problem, right?.
The only chance to protect against direct strikes is proper earthing. Wet soil
and rings of metal buried deep into the ground, if possible connected to
ground water. That way, the "range of destruction" can be shrinked to about
~10m around the pole.
So I don't think the optocouplers in the AAG equipment are for lightning
protection. They are for ground separation -- otherwise there would be a
noise-inducing ground loop between the PC, which *always* connects signal
ground to protective earth (major design flaw) and an auxiliary-powered
sensor outside.
Kind regards
Jan
--
Williams and Holland's Law:
If enough data is collected, anything may
be proven by statistical methods.
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