[Antennas] Lightning Protectors

[Eric Lemmon]

Jim,

Those old mechanical gap arrestors don't work very well, but I suppose
they are better than nothing at all.

The great majority of hilltop repeater antennas are DC grounded, so most
of the lightning stroke current goes straight down to Mother Earth
through the tower and the paralleled grounding conductors.  However,
there will still be several hundred- perhaps several thousand- volts on
the feedline to the radio, caused by the voltage drop in the tower. 
That is what a good surge arrestor is designed to reduce.  One of the
best surge arrestor designs, perfected by Huber + Suhner and others,
uses a replaceable gas-filled ceramic capsule that is very sensitive and
can carry gobs of current.

Surge voltages can pass right through the typical "pass/notch" duplexer,
since the coupling loops are insulated by the notch adjusting
capacitors.  A bandpass cavity has grounded coupling loops, and that
prevents those surge voltages from reaching the receiver front end and
blowing the RF amp or a PIN diode.

For HF antennas that are not DC grounded, the best insurance is a
grounding switch that completely disconnects the antenna feedline from
the radio and connects it to a good ground.

Article 810 of the National Electrical Code has some very good guidance
on installing and protecting Amateur Radio antennas.  It should be a
"must read" for all hams.  The NEC is issued every three years, and the
2002 edition is the current one.

73, Eric Lemmon WB6FLY

Jim Isbell wrote:
> 
> I have a very old coaxial lightning protector that has a ground screw on
> the side and a "gap" internally that is supposed to shunt lightning off
> the center conductor of the antenna lead in.
> 
> Do these work well?
> 
> Where is the best place to put them??
> 
> I dont understand how it would protect the equipment just because it
> shunted part of the lightning to ground.  Surely some would continue on
> down the cable to the receiver, wouldn't it??
> 
> - - -
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ antennas-owner@mailman.qth.net
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