Access Points and Lightning

[Jim Carter]

On Mon, 31 Mar 2003, Akash Heimlich wrote:
> I am wondering how lightning affects access points, in an outdoor
> environment...
> I know that lightning strikes the tower about twice a year...
> Next question:  what about the same setup but with a 1 m cable and
> directional antenna - does this increase the risk?

I think the risk would be the same.  The tower and its lightning rod should
be properly grounded -- the recommended method in the USA is a
copper-jacketed steel spike driven into moist ground, connected to the
lightning rod (not just to the tower) by big fat wire, around 6mm if I
remember right.  The signal cable should not be bundled with the ground
wire, but even so, a major common-mode surge will be induced in the signal
and power cables.

When I worked at the UCLA Tokamak Fusion Laboratory, we had major common
mode spikes on every shot, and up to 20 KV in a malfunction.  The
vulnerable instruments and ignitron controllers were isolated with homemade
optical isolators that could take the voltage, and control power was
provided through isolation transformers, again handmade.  The ideal for an
outdoor AP would be to bring the signals down on optical fiber.  But how do
you get power to it?  I'm not sure I trust commercial surge suppressors.

Perhaps someone in the tropics could post his/her experiences with
lightning vs. AP's. Someone in Darwin, Australia, perhaps?  Or Florida,
USA?  I, for one, would be interested to see what works in the real world.

James F. Carter          Voice 310 825 2897    FAX 310 206 6673
UCLA-Mathnet;  6115 MSA; 405 Hilgard Ave.; Los Angeles, CA, USA 90095-1555
Email: jimc at math.ucla.edu  http://www.math.ucla.edu/~jimc (q.v. for PGP key)