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Old 04-12-2012, 04:58   #1
TangoFoxtrot
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Faraday Cages ?

Home made Faraday cages, In your opinion do you think they really would work? If they are worth my time and money to build what do you think is the best type to construct?
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Old 04-12-2012, 06:35   #2
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Easy way to test, is to put a radio or cell phone in your cage & see if it works. (If the cage works, the radio or phone won't be able to receive a signal.)

Imperfect test as there are some differences between radio waves and em waves, but a test that can be learned from.
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Old 04-12-2012, 08:15   #3
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A Microwave oven is a Faraday cage. Place your cell phone inside, close the door and call your phone.

(don't turn the microwave on!!)

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Old 04-12-2012, 08:30   #4
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A radio test won't really prove a cage will protect against an EMP. The EM strengths are just too different by orders of magnitude. That's why EMP fries while radio signals do not.

Last edited by cowboy1964; 04-12-2012 at 08:31..
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Old 04-12-2012, 08:44   #5
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Yes, they will work. Yes, they are worth the time and expense (minimal) to construct if an EMP is something that is on your list of SHTF situations you are worrying about.
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Old 04-12-2012, 08:49   #6
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Faraday "cages" work on certain ranges of frequencies. Faraday boxes may work on all(?) frequencies. The size of the perforations determines frequencies they work to.
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Old 04-12-2012, 09:06   #7
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Best size of perforations imo is "zero" perforations; or a solid sheeting approach.

Quote:
Originally Posted by Glockdude1 View Post
A Microwave oven is a Faraday cage. Place your cell phone inside, close the door and call your phone.
I've heard that before but it didn't work when I tried it, so I never recommend it. Just out of curiosity, after reading your post I just now tried it again. Phone rang fine.


Best home-made version I've found is cumbersome & inconvenient, but works quite well, using paper bags & aluminum foil. To work, a faraday cage has to be conductive around the device, but istolated from it. Put the device in a paper bag, wrap the bag well in foil (fold the edges up good & tight), then another bag, another layer of foil wrap, then a third layer of the same. That's worked well for me in my admittedly non-scientific testing. Doing it that way, a supposed "12 mile" gmrs radio inside (turned on with volume all the way up), wouldn't receive from an identical radio even an inch away from the wrapped package.

Real downside to this approach is that it's a pain to get to the device. Only things I use it for are things intended to be put back in hopefully long-term storage, and a few things in my ghb gear. Doing so to protect ghb items (like night-vision, spare gps, etc) may be excessive or 'way out there', but to some degree the same could be said of having ghb gear in the vehicle in the first place.

If I had a way to test against genuine emp I'd do so, but that not being possible, this is the best & most conservative approach I've personally come up with. Always open to new ideas.
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Old 04-12-2012, 09:24   #8
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Quote:
Originally Posted by quake View Post

I've heard that before but it didn't work when I tried it, so I never recommend it. Just out of curiosity, after reading your post I just now tried it again. Phone rang fine.
Mayby microwaves are built different. I have a Stainless Panasonic 1250watt oven. I placed my Samsung Galaxy Note inside and tried it. Phone did not ring.

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Old 04-12-2012, 09:42   #9
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Quote:
Originally Posted by quake View Post
Best size of perforations imo is "zero" perforations...
Interesting post. Well my Ham Radio's "faraday" (ammo can) is getting some quake-style modifications ASAP.

My phone rings inside my microwave just fine. As casually as I could I said to my wife: "Oh, there it is, I must have forgotten it in the microwave." She was ready to have me committed on the spot and would not leave me alone until I gave an explanation. Followed by the "You're So Strange" look.
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Old 04-12-2012, 11:10   #10
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Quote:
Originally Posted by Glockdude1 View Post
Mayby microwaves are built different.
Could well be. Might be signal-strength issues, carriers, or even phone issues; no idea. Mine's a low-end LG (at&t) smartphone.
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Old 04-12-2012, 11:13   #11
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Microwaves (appliance) are designed to block microwaves Cell phones function on a number of different of frequnces based on your carrier.

What is the frequency of an atomic bomb EMP? How about a Solar Flare EMP?
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Old 04-12-2012, 11:31   #12
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Yes, they work. As others have said, there are construction/design criteria that need to be met.

Quake nailed it on the basic premise. You need to shield the device you want to protect, then basically insulate with non conductive material, then shield again.

I employ several anti-EMP technologies in my home.

First, the whole house exterior is a grounded, metal cage, independent of my interior ground. No kidding. Yes, I have windows, but their impact is minimal.

Basically I use a multi-layer approach. I cannot guarantee this will block all frequencies, as others have stated, but it certainly knocks a dent in major RF / EMP / power bombs coming my way.

Secondly, all sensitive electronics that I care about for EMP-proofness are handled in a variety of methods.

One method I like (and recommend) is the use of the aluminum/metal garbage cans. They hold a lot of stuff. The trick is to pack them in a way so that the internal compartment with your electronics is not touching the external trash can material. You need a good liner. I have tried various blankets and packing peanuts.

I do not have access to any serious test equipment that could put all my theories and practices to a 'real world' test, but I have done plenty of practical tests using my 20+ year background in radio.

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Old 04-12-2012, 11:46   #13
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I didn't know that a second metal layer was needed. I want to find out more. FWIW, I have a metal shingle roof. It blocks signals in the attic and upper bedrooms.

I always wondered what lightning would do to an EMP barrier, would foil protect or would the heat/voltage blow right through.

Will it stop those voices in my head that I keep listening to? They can get pretty annoying, sounds like my wife.

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Old 04-12-2012, 14:03   #14
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Quote:
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I didn't know that a second metal layer was needed...
Can’t say about “need” since I don’t know a truly accurate way to test for emp; so I just go with ‘more is better’. When testing with the gmrs radios (and department portable radio, and cell phone and AM & FM radios), more layers blocked better. Seems obvious, but good to see the principle in action rather than just in theory. Example, with the gmrs, inside a single layer of bag-then-foil, the radio would pick up from a range of 10-15 feet (these were alleged “12-mile” radios). With a second bag-then-foil layer added, it took reception down to a few inches. A third layer took it down to zero. Seeing that two worked that much better than one and three worked better than two, I went with three to be safe.

Frankly, seven or eight layers wouldn't hurt imo if it was something critical and/or hyper-expensive that you could live with leaving in seriously-long-term storage. If I had some unique, life-critical item that I absolutely wanted to protect to the absolute best of my ability, I'd do as many layers as would fit inside whatever chosen outer container (garbage can, ammo can, rubbermaid tub, etc) just to be safe. May not be necessary, may not even be beneficial or even helpful; but I figure it couldn't hurt.


Fwiw, one experiment I tried that really surprised me was with brass window screen. Not the plastic or even aluminum stuff you typically encounter, but genuine brass window screen. I took a small section of that - probably a foot or so square - and rolled it into a tube shape about 4" in diameter & a foot tall. Left the ends open, just a short section of screen tube. My dept radio has the NOAA weather channel programmed in, and leaving that channel running, just slipping the tube down around the standing radio was enough to completely kill the signal. I was very surprised at that (it was my first hands-on testing), but to be fair, we're pretty rural and the signal wasn't as strong as it probably is in some areas. Doing the same thing with a gmrs radio or cell phone had no noticeable effect on reception at all, but with the noaa, am or fm, it killed it.


The point of all this rambling & babbling is "test stuff"; and then let us (everyone) know what you find. I'm happy if someone can learn from me, but I'm much happier when I can learn from them.
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Old 04-12-2012, 18:18   #15
DoctaGlockta
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Quote:
Originally Posted by Glockdude1 View Post
A Microwave oven is a Faraday cage. Place your cell phone inside, close the door and call your phone.

(don't turn the microwave on!!)

Well you got me to at least try it.

Call went through however.
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Old 04-12-2012, 18:53   #16
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Quote:
Originally Posted by Glockdude1 View Post
A Microwave oven is a Faraday cage. Place your cell phone inside, close the door and call your phone.

(don't turn the microwave on!!)

I don't believ so. Oven door is glass after all and faraday needs to be metal all around...need proof please.
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Old 04-12-2012, 18:57   #17
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Quote:
Originally Posted by RED64CJ5 View Post

First, the whole house exterior is a grounded, metal cage, independent of my interior ground. No kidding. Yes, I have windows, but their impact is minimal.
Red, I value your opinion and expertise, please elaborate on the above..what do you mean that your house is grounded in a metal cage?

Thanks


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Old 04-12-2012, 19:28   #18
Glockdude1
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Quote:
Originally Posted by sebecman View Post
I don't believ so. Oven door is glass after all and faraday needs to be metal all around...need proof please.
My Stainless Panasonic microwave block the signal on my cell phone.

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Old 04-12-2012, 21:50   #19
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Quote:
Originally Posted by sebecman View Post
I don't believ so. Oven door is glass after all and faraday needs to be metal all around...need proof please.
It is glass with embedded metal that is perforated. The holes are large enough to allow you to see through it, but not large enough to allow microwave frequency radiation through it.
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Old 04-13-2012, 00:18   #20
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Have you seen this movie? It has a pretty good Faraday cage theme to it.

The Darkest Hour

http://www.imdb.com/title/tt1093357/



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