[TowerTalk] Fwd: Shielded shack

Sat Sep 28 14:56:44 EDT 2013

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.
>
> My idea is to protect the gears inside the shack when lightning strikes the tower. I don't believe the current going through the foil will be that high. It is determined by the capacitance between the shack and the ground, and the rise time of the voltage, right.

Lightening has punched holes (sometimes large) through Airplanes as they 
happened to be "in the way.  I don't think foil on a grounded structure 
would offer much protection.

A good grounding system and a SPG at the shack entrance are the 
important points.

>
> Presently, I have an aluminum plate under my radio equipment to which everything is grounded. The plate acts like a "half" Faraday shield, and I believe that arrangement saved me a couple of times. (I have had three (3) know direct strikes in my house and have learned the hard way how to protect electronics; telephones, stereos, etc.) I have not lost any ham equipment yet.
>
>
> Grounding of the foil will be via a conductor connected to the tower. Hope that is not against any code.
>

Any connection to the foil would need to cover a relatively large area 
such as an Aluminum plate of several square feet with the connector on it.

The first 6 years after installing the tower and ground system, it took 
an average of 3 visually verified hits per year for a total of 17 as 
reported by neighbors.  The tower is a 100' ROHN 45G with a 30' DOM 
steel mast holding a TH5, 7L 6-meter C3i with a close to 30' boom and a 
14' cross boom on top at 130 feet holding a pair of 11L 440s inboard of 
a pair of 12L 144s.  That was way too much above the top of the tower. 
After seeing them whipping as much as 30-40 degrees in a strong wind, 
I'm amazed the top antennas held together.

http://www.rogerhalstead.com/ham_files/Tower29.htm  and
http://www.rogerhalstead.com/ham_files/Tower26.htm

Right now all the antennas are down for maint and satellite dishes are gone.

Plus I'm installing an LM470 crank up in the place of the small tower at 
the end of the shop.  These are all tied together with over 600 feet of 
bare #2 with 32 or 32 ground rods CadWelded to it.

73,

Roger (K8RI)

> 73 de,
>
>
> Hans - N2JFS
>
>
>
> -----Original Message-----
> From: Roger (K8RI) on TT <K8RI-on-TowerTalk at tm.net>
> To: towertalk <towertalk at contesting.com>
> Sent: Sat, Sep 28, 2013 11:56 am
> Subject: Re: [TowerTalk] Shielded shack
>
>
> 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.
>>
> 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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