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Re: [TowerTalk] Shielded shack

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Shielded shack
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Sat, 28 Sep 2013 11:55:20 -0400
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On 9/28/2013 1:51 AM, Grant Saviers wrote:
If it is lightning protection and not RFI shielding that is desired, then what is done for explosive magazines ought to be enough! http://www.seftim.fr/publications/DDESB/17-3-LIGHTNING_PROTECTION_FOR_CRITICAL_EXPLOSIVES_OPERATIONS.pdf has many references, but there are older documents I've seen in prior google searches. e.g. http://www.apd.army.mil/pdffiles/p385_64.pdf Or standards for protection of petroleum storage facilities.


Although I guess you could call it a Faraday Cage, these really are not effective at the frequencies operated (160through UHF), but I'd think a fairly effective lightening protection protection cage could be built using #3 rerod (about 5/16ths) with the rods laid out using 6" to 12" spacing, (my personal preference = 6")vertical and horizontal with each crossing junction welded. I'd make the door the same way with it bonded on the hinge side using copper braid with the other side camming tight against a conductive vertical member The whole thing could be covered with aluminum window screen (on the inside of the rerod) to create a real Faraday cage although I don't see any advantage in doing so.. I'd cover the outside with Vinyl siding for appearance. Finish off the inside like normal construction. You are probably looking at $300 +/- for rerod and welding every junction is a lot of welding although each weld is small.

Remember you are building a cube and all 6 sides need to be covered.

IE: It's just a stick built room covered with a grid created out of rerod for lightening protection and a LOT CHEAPER than using copper unless you don't have a welder and have to hire that done. That is a lot of rerod.<:-))

I'd pitch the foil idea. Hard to bond reliably, fragile, and very little current capacity before vaporizing and setting the "shack" on fire.


I would add, that if the tower or shack ever takes a direct hit, your ears will likely ring for an hour or so. Course, good insulation is also good sound proofing.

73

Roger (K8R)

I would also think that foil is a bad choice as a conductor should you have a strike when #2 or larger is what is commonly used in large structures frequently hit.

On 9/27/2013 8:05 PM, Hans Hammarquist wrote:
Gentlemen,


I am on the process to build myself a (small) free-standing shack next to my tower. I am thinking (which usually is dangerous) that I should "dress" my shack in aluminum foil, making it into a large Faraday Cage/shielded room.


By connecting the foil to the tower and make sure all wires entering my shack enters through a (relatively) small window I should be able to make the ultimate lightning protection.


What can go wrong with this? The foil will be connected through-out, walls, floor, ceiling. All the feed-through connectors, surge protectors etc will also the connect to the foil. I will using a wide aluminum strip to connect the tower to the foil. Yes, the tower has nine (9) gounding rods, so I believe that is OK.


Any feedback?


73 de,


Hans - N2JFS
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