Yes Jim, the "single point" is not really a single point. In my case it is a
single, conducting panel that has feed-through coax connectors and surge
protections for all other wires coming through the panel. I plan to use gas
discharge for signaling and MOX for power (Done that before with good result.
Yes, it was tested with real lightnings.). The panel will be connected all
around its perimeter to the shield.
I still don't know what shielding to use. You are right that attenuation for RF
radiation is low for the RF from a lightning strike. Al foil is still
attractive especially as it is readily available (supermarket) but I wonder if
I should add in wire mess as well.
Good I don't have to decide today.
Best 73 de,
Hans - N2JFS
-----Original Message-----
From: Jim Lux <jimlux@earthlink.net>
To: towertalk <towertalk@contesting.com>
Sent: Sat, Sep 28, 2013 6:33 pm
Subject: Re: [TowerTalk] Fwd: Shielded shack
On 9/28/13 11:56 AM, Roger (K8RI) on TT wrote:
> On 9/28/2013 1:27 PM, Hans Hammarquist wrote:
>> The idea is not to let any current through the aluminum foil. ALL
>> connections to the foil is in ONE point, the point there everything is
>> entering the shack. I do not believe tht the foil would protect the
>> shack from a direct lightning strike. What is the possibility that
>> will happened anyhow with a 85 foot tower next to it. OK, never say
>> never!
>
> This is where the Single Point Ground (SPG) is important and that every
> lead coming into the shack is protected. Power, if multiple circuits
> needs to follow the sane routes for their entire lengths. Use a
> relatively large, grounded, "bulkhead" through which all leads must
> pass. Grounding and bypassing all leads is to insure the induced
> voltage from nearby strikes causes the voltage on all lines to rise at
> the same rate and to the same potential. Your common grounding sounds
> good.
One should abolish the term single point "GROUND", because it isn't
ground. "common voltage reference point" would be a better term.
But the description here of everything (power, phone, data, coax) coming
in tied to a common point is sound. It doesn't physically have to be
through some sort of bulkhead. But it does need a low resistance,
reasonably short connection.
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