[IRCA] Lightning-resistant antenna coupling

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

One of the significant problems with spring and summer DXing is the threat
of lightning.  I have made something which significantly reduces that
threat.

I bought two large ferrite rods for experimenting some time back.  What I
did was set one vertically, which has minimum pickup of signals in itself.
This is connected to the antenna coax.  Another identical rod was positioned
about a foot away, also vertical.  This was connected to the receiver.  The
mutual coupling beween the two allows significant signal to be passed
between them.  In practice, I cannot see much difference in S-Meter level
between this arrangement and a direct connection to the receiver.  Since
they are separated by about 12", the chance of a lightning strike jumping
that gap is very minimal.  Kind of like an isolation transformer.

One problem remains of the lightning strike generating a very intense
wideband RF signal.  I will buy a gas suppressor Monday, probably an Alpha
Delta ATT3G50U or Diamond CA35RS.  That should clamp incoming RF to a safe
level.

A couple of side benefits..  I notice noise has dropped a significant
amount.  Second is that it would be possible to put one rod (waterproofed,
of course) outside and the other inside.  The signal ought to pass through a
normal wood wall just fine.  Great for temporary hookups without drilling
holes.

The two ferrite rods are about 20" long, though smaller ones would no doubt
work fine.  These have five turns of #14 wire connected to an SO239 jack.
There is a ferrite choke between the rod and the jack.  This provides a
common mode rejection and effectively balances the connection.

Hope it proves useful..

Craig Healy
Providence, RI

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