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Gun safe as a faraday cage

Discussion in 'General Gun Discussions' started by battlecry, Feb 29, 2008.

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  1. battlecry

    battlecry Member

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    Locked my cel phone and home wireless phone inside the safe. Dialed them and I could hear them both from outside the safe :eek:

    I had a feeling the door gap could pass RF or microwaves but finding out was a letdown. I am going to order some 3M embossed EMI tape to place around the door and report back. Hopefully I can make it an OK place to store some radios and such.
     
  2. Dave P

    Dave P Member

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    Uh, why??

    Huge gaps around the door will let in a lot of energy. And unless you want to strip off the paint at the joints (to get low impedances) , the tape won't help much IMO.
     
  3. TexasRifleman

    TexasRifleman Moderator Emeritus

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    You worried about an EMP or something?

    I've heard, though never tested it, that a microwave oven makes a decent Faraday cage.
     
  4. battlecry

    battlecry Member

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    My cell phone works inside my microwave oven :confused:

    Makes you wonder.
     
  5. 41magsnub

    41magsnub Member

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    May I ask how you tested that? Does it work while it is running?:neener:
     
  6. DoubleTapDrew

    DoubleTapDrew Member

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    Why are you concerned about RF frequencies getting inside? Would an EMP from a nuke or something permanately damage electronics or do they shut down until the pulse passes then work again? I've always wondered that. If they are permantely damaged it's not like there will be any radio broadcasting going on anyway.
    Seems like there would be better options than a gun safe for protecting against that. Some people use tinfoil hats :p
     
  7. musher

    musher Member

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    Don't you need to ground the safe to make it work?
     
  8. GhostlyKarliion

    GhostlyKarliion Member

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    the key component to a faraday cage is that it's grounded and has no pass through holes larger than the desired frequency, a solid metal box will work fine, as long as it's grounded.

    try getting a small sheet metal screw and driving it into an inconspicous part of the safe, wrap a copper wire around it and either get a plug from wally-world to wire the ground to (please make sure you stick it in the ground, the single hole below the other two) or just stick the other end of the wire in the ground socket in a plug, odds are that the safe isn't grounded anywhere.

    also, instead of using tape for the door, you could install cut pieces of metal around the door openings, but your safe shouldn't be leaving any light passage holes anyway.
     
  9. strat81

    strat81 Member

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    Did someone mention tinfoil hats?
    [​IMG]
     
  10. Deacon Blues

    Deacon Blues Member

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    Are you worried about the FBI spying on you? I find it highly unlikely that anyone is listening through my wife's cell phone, but I don't like the idea of enabling it through inaction. My microwave oven does work, although surprisingly a steel ammo can does not. :scrutiny: You could always construct a metal sleeve of some sort for the phone.
     
  11. Snagglepuss

    Snagglepuss Member

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    I thought an EMP only damaged electronics that were in use. If the radio is off, not plugged in or without batteries, there would be no damage. This is just what I thought, not what I know.
     
  12. Cesiumsponge

    Cesiumsponge Member

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    Needs to have a very good RF/earth ground if you want to protect something I assume is quite valuable. You'd probably want to stake your own dedicated ground in the backyard with a network of 8' copper pipes driven into the ground. Consult some ham radio guys on how to make a good, dedicated ground.

    Devices that aren't powered can still be damaged. The pulse creates incredibly high energy densities and it'll induce high voltages in anything wanting to be a receptive antenna. Considering semiconductors in general operate at voltages of 12VDC or lower, it wouldn't take much to damage them.
     
  13. benEzra

    benEzra Moderator Emeritus

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    No, EMP fries things by the induced current pulse. The pulse usually isn't big in absolute terms, but is big enough to fry transistors on a microchip, and whether it is turned on or off is irrelevant.

    You may be thinking about power surges, which are transient overvoltage conditions in your wall AC that can fry something that's plugged in and turned on. But that's not EMP.
     
  14. Sixtigers

    Sixtigers Member

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    The last couple of posts were spot on. A strong enough EMP burst ruins your electronics by inducing huge (comparitively) voltages across solid-state microcircuitry--basically, anything with chips. Standard solid state stuff--resistors, capacitors, chokes/coils, etc...and most transistors are large enough that the voltages involved don't do any damage. Microcircuitry, however, or 'chips'--that's a different story. A microchip is basically anywhere from four to several million transistors--little teeny-tiny transistors, microscopic in size. Ever walk across a carpet, then touch a doorknob? That shock you feel is on the average of about 50,000 volts. Very little amperage (thank heavens!), but very high voltages. An EMP burst generates these same differences in electrical potential (or 'voltage')That voltage blows big craters (well, microscopic craters, actually...but you get my drift) in the "world of teeny-tiny transistors", or microcircuitry. If you put an ESD damaged chipset underneath a microscope and observe the damaged area, that's exactly what it looks like. Like bombs went off in microcircuitry land.

    These damaged chips can no longer function. Unfortunately, it does not matter whether or not your solid-state device is plugged in or not, or powered up or not--the EMP burst travels through the air. Thankfully, it's usually fairly localized. However, if an EMP burst takes out a power plant or telecommunications facility, the fact that your personal electronics may function does you no good, without power or access. And that's the true danger of an EMP burst.

    I don't know if a solid-steel, grounded box would work as a faraday cage. The most important thing is the grounding--that cannot be overemphasized. When these guys tell you to hook it up to house ground, by all means--do it. But NOT through a household 115V AC socket's ground connection. If you want a successful cage, you need to connect to your house's actual grounding point, and you need to do it with some serious cable. I'm looking at the cabling we use for our cages here at work, and for our ESD benches, and the grounding cable is composed of stranded copper line (think automobile battery cables, only where the individual strands are the same gauge as the wire in clotheshangers) approximately 1/2" thick, 3/4" in some instances. The copper rod pounded in behind the shop is about 12 feet long, and provides our ground.

    Our (I'm a military contractor) faraday cages are made out of copper cloth. I'm not an engineer, and don't quote me, but I'm fairly sure that a solid-steel cage isn't as effective as a grid--something to do with induced voltages across a grid draining more effectively than what is, effectively, a big friggin' antenna. Key factor: Grounding.

    Not sure why you'd want to save your cell phone, anyway. In the event of an EMP, I'm thinking cellular communications won't be viable. An extra computer/ECU for your car, a hand calculator (or two), maybe hand-held talkies/CBs and shortwave trunk scanners...that kind of thing, sure.

    The gentleman that are pointing out that your 'cage' must be grounded
     
  15. atblis

    atblis Member

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    Just wrap your phone radio in Aluminum foil. Grounding isn't needed.
     
  16. DoubleTapDrew

    DoubleTapDrew Member

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    That's a dang good idea. However if you were the only working car on the road I think you wouldn't want to be anywhere near it if you ever plan on dropping below 60mph
     
  17. Dravur

    Dravur Member

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    I keep

    my dog in my safe, cuz it is spying on my from the chip in his head. The FBI put it there.

    If you have an EMP pulse in your neighborhood, you might have some other problems....
     
  18. Thin Black Line

    Thin Black Line Member

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    If you're close enough for EMP to fry your electronics, you'll probably also be
    close enough to the blast to feel some of the heat and experience the
    subsequent fall-out to not worry about listening to the radio afterward.
     
  19. TexasRifleman

    TexasRifleman Moderator Emeritus

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    One of the fears during the Cold War was a space based detonation of a nuke for just this reason.

    A 120km altitude detonation could have an EMP range as far as 1000km
     
  20. brickeyee

    brickeyee Member

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    It does not take much metal to attenuate an EMP pulse.
    0.060 aluminum does a good job for the fast rise time pulses.

    The biggest problem is holes and joints in the 'skin'.
    The magnetic portion of the pulse can produce a large voltage across any joint that is not suitable bonded (and the bond needs to work at the frequencies of interest, think many 100s of MHz).
    Opening must be less than 1/10 of the wavelength for the same frequencies.

    The most common way to protect equipment is to use a nuclear event detector (NED, just a phototransistor in a metal can) to immediately crowbar the power supplies.
    With no power and a decent enclosure electronics survives rather well.

    Long conductors (think power lines) are harder to protect.
    They can couple very large voltages and currents from the pulse, and fuses are often way to slow (milliseconds) to respond to the pulse (nanoseconds) before damage is done to transformers and other devices with insulation.


    As for range and blast proximity, the ideal way to create a destructive EMP pulse would be to set off a nuke at the edge of the atmosphere above the target.
    Even places slightly past actual line of sight from the detonation will get slammed by the pulse.
    Set one off over the middle of the US and you could disrupt things from coast to coast with no other damage on the ground.
     
  21. OMGWTFBBQ

    OMGWTFBBQ Member

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    Neither here nor there.
    If you need a cheap Faraday cage for small stuff, just take an ammo can and coat the inside with Plastikote truck bed liner or something else that will serve as an insulating barrier, hell, you don't even need to get that fancy, it should do for radio equipment and such.
     
  22. MaterDei

    MaterDei Member

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    If you can remove the antennae on your phones, that will help.
     
  23. hqmhqm

    hqmhqm Member

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    I don't understand why grounding the cage makes any difference at all to what is inside. Is it voltage difference across the components inside that kills them, and the faraday cage is a shield that makes a uniform voltage over it's surface. It should not matter too much what the "absolute" voltage level is. It's like when those guys work on live power lines, as long as they are the same voltage as the line, there is no voltage difference, and hence no damaging currents. In fact in that case you don't want to ground the guy, you want him to float up to the voltage he is working on.
     
  24. sacp81170a

    sacp81170a Member

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    I ground radio and computer equipment the old fashioned way, through the plumbing. Water supply lines(especially copper) are great and you can get grounding straps for them at most hardware stores. Alternatively, you can buy a copper sheathed steel grounding rod about 8 feet long at Lowe's, pound it into the ground until only a couple inches are sticking out and ground to that. The advantage of using your home's plumbing is that condensation on the pipes makes even better contact with earth than a dry grounding rod. When we put the grounding grid in for my server room, they installed a drip system to keep the ground moist and provide reliable contact.

    Good for shielding M6 blasting caps from RF when onboard aircraft, too. ;)
     
  25. RoadkingLarry

    RoadkingLarry Member

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    Nuke 'em from high orbit, it's the only way to be sure!
     
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