[Elecraft] Silly arrestor question

[Don Wilhelm]

Michael,

If you are trying to predict the behavior of lightning, I suggest that you
stop - that stuff is as unpredictable as anything I have run across.

I would think that protection for lightning must consider not only the
differential surge, but the common mode as well.

The common mode surges can be addressed by proper grounding of the coax
shield at the station antenna connection grounding point (entrance ground) -
while devices like the PolyPhaser suppressors handle the differential
voltages (or gas discharge tubes, etc.).

There really is no concise answer to your question - lightning behavior is
unpredictable IMHO, and I have seen that unpredictability a couple times -
for my part, either provide adequate station grounding which is designed for
lightning strike dissipation or disconnect the antennas well before the
lightning storm approaches.

I have a perimeter ground wire with grounding rods around each of the
buildings on the property that the coax lines enter, and I use PloyPhaser
suppressors at the initial entry point with a multi-ground rod connection.
I use a single grounding window entry point for everything in the shack
(ethernet, phone, antennas, AC power) and still I choose to ground my
antennas (my remote antenna relays ground all but the active antenna) and
not operate when a lightning storm is in the vicinity - I'd rather be safe
than sorry - I don't know for certain that my measures are adequate, so I
take steps as though they are not adequate.

73, Don W3FPR


> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of Masleid, Michael
> A.
> Sent: Monday, January 09, 2006 4:25 PM
> To: elecraft at mailman.qth.net
> Subject: [Elecraft] Silly arrestor question
>
>
> I see that a coaxial line arrestor has a gas discharge tube
> between the center
> conductor and the coaxial shield.  The other stuff, inductors,
> resistors, capacitors
> are important, but not interesting during a lightning strike.
> All of this stuff is in
> a thick conductive box.
>
> This may sound like a dumb question, but think about it.  How
> does the lightning
> get out?  The walls are several skin depths thick.
>
> There seems to be a ground lug on the outside of the box.  That
> would take care
> of current on the outside of the coaxial cable well enough.
>
> Wouldn't the voltage and current running between the center
> conductor and shield
> have to reflect back up the coax, and then come back down the
> outside of the cable
> to get to the ground lead?
>
> Michael, AB9GV
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