Antenna grounding help
scooterspal wrote in news:kqWHh.8733$jx3.6472
@newssvr25.news.prodigy.net:
....
I have a gas discharge unit that comes with the antenna. It mates to
the
bottom connector and terms with the connector for the 4' of coax wire
that leads through the wall to the wireless AP unit. There is a ground
lug on the side of the discharge unit to attach a lead to.
....
Effective lightning protection is not trivial. It starts with an
assessment of the risk, including whether or not your structure is
effectively protected by nearby structures. The design of a protection
system should be an integated design, what you do to your antenna may
impact the other antennas / conductors / structures that are co-located.
Keep in mind that protection conductors may need to withstand typically
20,000A for 0.1s. The coax outer will probably not withstand that, so you
must route the discharge to ground a different way.
The gas discharge unit is to limit the voltage rise on the inner
conductor of the coax wrt the outer conductor. I think that it would be
unusual that a gas discharge device would be effective unless / until the
antenna / feedline was damaged, due to device's slow ionisation time and
the rather small voltage with fast rise times that would be induced in a
narrow band 2.4GHz antenna. It seems to me that your principle hazard is
the current that will flow on the outer of the coax as a result of a
direct or nearby strike, or the potential difference between your coax
outer and the building earth system in the event of of a direct or nearby
strike.
I know they sell these protection devices for the purpose, but I do
wonder about their effectiveness.
Routing the discharge current effectively to ground is important, but
equipotential bonding to avoid potential differences at critical
interfaces is an important part of solution design.
So the first stage of the solution is to prevent most of the discharge
current following the coax into the equipment room.
I agree with all that Jim Lux has offered you.
Owen
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