[time-nuts] GPS antenna and lightning
usenet at teply.info
Sat Sep 26 14:07:59 UTC 2009
Am Saturday 26 September 2009 14:44:52 schrieb Robert Vassar:
> Nothing will save you from a direct strike. At least nothing you can
> likely afford. You're more likely to get clobbered by a surge from
> the grid, or induced voltage from a nearby strike.
> Use the "box method". Draw a diagram of your equipment, then draw a
> large box around it. Any wire that enters or leaves the box requires
> some kind of protection device. In the case of a GPS antenna, likely
> a relatively expensive gas discharge tube bonded to a properly
> installed ground rod by a short length of heavy copper braid.
I'll second that. First, a nearby hit is much more likely than a direct one.
And even though there are some standard tests, at a direct blow all bets are
off anyways. So the most likely way to have equipment affected by lightning
is in fact induced voltages/currents from nearby strikes.
The "box method" described by Robert is actually (IMHO) the only approach that
is usable, even though i myself would introduce more than one level of boxes.
Over here (Germany, that is), the most common approach has three or four
levels of boxes with their own protection levels. The outermost box will thus
handle the most severe stuff and limit exposure to overvoltage for the inner
levels. So, the inner protection devices don't have to handle a real hit but
only "minor" overvoltages, which occur much more often that the really scary
ones. Chances are, that a strike won't reach the innermost level of
protection, and due to the spread of protection over a couple devices, one
failing won't kill your equipment.
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