On Sun, 12 Mar 2006 10:59:56 -0500, "Robert11"
wrote:

Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

Your station can be thought of as a cluster of "black boxes" with
interfaces (eg power, audio in, rx RF in, control, etc) that are
suceptible to damage if large voltages are impressed across those
interfaces.

Hardening a station against lightning usually involves minimising the
voltage impressed across those interfaces in the event of lightning,
and two main approaches are followed (usually together):
1. - reducing the current that enters the station in a strike; and
2. - reducing the voltage drop in conductors within the station that
would cause high voltages across interfaces.

Item 1 is usually done by diverting the bulk of the lightning current
via an alternate path to ground. This means shunting the current
through a low impedance path to ground before it enters the station.
Series impedance on the path to the station may assist in increasing
the portion of the strike current that flows by the alternate shunt
path to ground, but series impedance without the upstream shunt path
is not likely to have much effect. The series impedance you propose is
very small, so its effect will be quite limited.

Item 2. is usually addressed by the design of the earthing system and
equipotential bonding (eg single point earthing).

In summary, a one turn loop in the coax alone is not going to provide
a significant improvement in lightning protection in a station that is
not otherwise hardened against lightning or EMP.

Owen
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