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Survival and Preparations Long and short term survival and 'prepping'.

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  #1  
Old 05-18-2017, 10:04 AM
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Default Metal pole barn = EMP safe?

I see a lot of pole barns that have sheet metal roof + sheet medal sidings... makes me wonder if that acts as a Faraday cage.
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Old 05-18-2017, 10:27 AM
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Large cracks in soffit area big enough for birds to get through.
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Old 05-18-2017, 11:47 PM
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For a faraday cage, you need metal coverage all around, including the flooring.
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  #4  
Old 05-18-2017, 11:49 PM
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Sure as long as it is copper building with no windows in structure, has a copper floor and no doors open. And you are far away from emp origination point.

Last edited by edgerly779; 05-18-2017 at 11:52 PM..
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Old 05-19-2017, 12:18 AM
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Quote:
Originally Posted by TrailerparkTrash View Post
For a faraday cage, you need metal coverage all around, including the flooring.
It really depends on what you are trying to keep out. EM signals (pulses) have an amazingly hard time going through dirt.

If you are trying to make a RF clean lab for the purposes of doing weak signal analysis on new hardware, then yes, you have to do the floor. If you are worried about your car shorting out then it would take take anywhere near as much

Don't believe me though, it's pretty easy to do the experiment yourself with two handheld radios. Use one outside and one inside and see how weaker the signal is inside when transmitting from outside. The same principle works with an EMP, since it effectively is just a really loud radio blast.

(Make sure your radios are properly liscensed.. Yada yada)
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Old 05-19-2017, 8:00 AM
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Low frequency is easy to block. High frequency not so much.
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Old 05-19-2017, 8:49 AM
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I did some testing with my "un-licenced" ht's using a galvanized trash can and hvac aluminum tape.

No rx from keyed ht from across the yard@5watts.

AM radio rx was nil.

The hvac tape seemed to play a key part in sealing the signals out. *Tried without tape at first.

Radios were resting inside a clay pot and set inside the can. Antler sticking straight up.

This diy principle seems to be worthy of further exploration.

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Old 05-19-2017, 9:19 AM
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Any amount of grounded metal will attenuate an EMP somewhat. How much attenuation you are looking for is the question. If you're looking to just keep your car's computer from frying, a metal barn would probably do the trick (your car's computer is already enclosed in a grounded metal box, and your car probably already has a metal body). If you're looking to protect super sensitive electronics, then a continuous cage would be necessary.

Where you're located is also a factor. EMPs are generally line of sight, so if you live in the flatlands, you're more susceptible. If you live deep in a canyon, you're less susceptible (unless the EMP originated directly above you).

In any event, if there were an EMP big enough to warrant discussions like this, we probably have bigger problems than starting a car - the grid would be fried, and communications would be down (except for shielded radios).
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Old 05-19-2017, 9:31 AM
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I live in a forest canyon and when in the metal sided, framed, roofed garage which has 2x4 10ga remesh in the 5" concrete slab my phone essentially does nothing. Step outside the door and all is fine. That's the way it ended up, not that I planned anything relative to radio signals. It works pretty much the same in the much larger clearspan metal building at my CA place. To get wifi from the repeater on the office I needed to put a receiver router with external antenna on the shop.
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Old 05-20-2017, 3:20 PM
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Quote:
Originally Posted by Epaphroditus View Post
Low frequency is easy to block. High frequency not so much.
So which one applies to one single pulse?
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Old 05-20-2017, 3:29 PM
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Pulse is generally lots of high frequency. Never looked at power spectrum of various pulse forms? Interesting stuff.
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Old 05-21-2017, 8:06 AM
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EMP pulse as I understand it for offensive weapons is bomb-based, creating one giant emission from an explosively collapsed magnetic field, and the aparratus is destroyed in the process, I'm not seeing the source for multiple waves.
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Old 05-21-2017, 8:43 AM
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Here's a no BS assessment about the science explained during actual testing. The "Myth" section (follow the linkage) is very helpful IMHO.
Best info I've found to date.
http://www.futurescience.com/emp.html
Quote:

Nuclear EMP is actually an electromagnetic multi-pulse. The EMP is usually described in terms of 3 components. The E1 pulse is a very fast pulse that can induce very high voltages in equipment and along electrical wiring and cables. E1 is the component that destroys computers and communications equipment and is too fast for ordinary lightning protectors (although devices that are fast enough are routinely being produced, but are rarely used in the civilian infrastructure). The E2 component of the pulse is the easiest to protect against, and has similarities in strength and timing to the electrical pulses produced by lightning.

The E3 pulse is very different from the E1 and E2 pulses from an EMP. The E3 component of the pulse is a very slow pulse, so slow that most people would not use the word "pulse" to describe it. The E3 component lasts tens to hundreds of seconds, and is caused by the nuclear detonation heaving the Earth's magnetic field out of the way, followed by the restoration of the magnetic field to its natural place. The E3 component has similarities to a geomagnetic storm caused by a very severe solar storm.
Sent using a long string and 2 Dixie cups (EMP proof)
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Last edited by FeuerFrei; 05-21-2017 at 10:58 AM.. Reason: added linkage and quote for S&G's
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  #14  
Old 05-21-2017, 10:15 AM
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Now I not only want a pole barn, but a giant faraday cage too. Thanks!
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  #15  
Old 05-21-2017, 12:44 PM
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Quote:
Originally Posted by FeuerFrei View Post
Here's a no BS assessment about the science explained during actual testing. The "Myth" section (follow the linkage) is very helpful IMHO.
Best info I've found to date.
http://www.futurescience.com/emp.html

Sent using a long string and 2 Dixie cups (EMP proof)
OK fine, so we have 2 distinct waves? How far apart?
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Old 05-24-2017, 10:06 PM
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I have built several Faraday Cages for testing & R&D of various radios. If you really want a Faraday Cage, bury copper mesh under the dirt floor, connect it to copper mesh fully enclosing your area. Nothing else will be the same, even using a metal trash can is not the same. If your just looking for "just enough protection" you are probably fine with your metal building. You could make it a little better by filling any gaps or seams with copper mesh. The most important part is a good solid ground, dig deep and cover with rock salt. Make sure nothing you want protected should be allowed to touch or even be next to the cage.
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