Posted: 2/9/2008 1:16:51 PM EDT
| Is it true or false that by placing electronic items in a metal ammo can you can shield them from EMP and thus have working electronics after an EMP event? |
most electronics items that fit into an ammo box will not be affected by EMP -- PROVIDED they do not have long metallic leads connected to them, such as power cables, antennas, and so on. for more info on EMP effects (or not, as it may be) on small electronics, click here ar15.com/forums/topic.html?b=10&f=22&t=604477 and scroll all the way down to the post titled "EMP and Ham Radio". for more info on what REALLY constitutes shielding, click here ar15.com/forums/topic.html?b=10&f=22&t=609246 ar-jedi |
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I just posted a 7-page article on EMP today here: www.ar15.com/forums/topic.html?b=10&f=17&t=609320 |
I will agree. I did a simple test, I but my cell phone in one, then I called from a land line. it rang.  I then but a gmrs radio in it, I hit the call on another gmrs radio outside the box, and I could here is rx'ing the signal. If such low power can get thru, then emp will not get stopped. |
Great article! In short though, the answer is yes, a metal box will shield a small solid state device from EMP. |
In the aftermath of such an event you will have much bigger things to worry about than small electronic devices. The retaliatory strike and likely escalation to full out nuclear war is what you would need to plan for, assuming you survive at all. If you haven't read "Lights Out" I can highly reccomend it as both enjoyable fiction and a glimpse of what we may have to deal with if "only" the high altitude burst happens. |
If its plugged in, or has a decent sized antenna then it is quite likely to be destroyed. If putting electronics into ammo cans makes you feel better then have at it. I'll just go get some more grub stacked up and a couple extra cases of water. |
Might be nice to have a radio though. Might be good to get some news. What harm would it do to throw a radio, maybe a little battery powered clock in an ammo can? |
No harm at all. As long as the antenna isn't hooked up to the radio while its sitting on the desk, then it'll probably be okay anyway. Then again, I'm running low on ammo cans. They are all full of ammo & mags. Need to order some more I suppose.... ETA: Make sure the can gets a good seal, and throw some desiccant in there, waterproofing would be an added benefit. 
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| I know that Airborne Command Post type airplanes have a trailing wire antenna that they can spool out to transmit HF Radio to burn through radiation/fallout in the atmosphere in the event of a nuclear attack. If your cell phone, or radio make it through a EMP, who will you be able to talk/listen to? |
you are outside your domain of expertise here.
other people with functioning radios. ar-jedi |
I don't have any expertise here, it was a question. I will rephrase the question, forget the trailing wire antenna; after an EMP event, you take out your shielded cellphone and since the cell towers and everyone else's cells weren't shielded, who do you talk to? |
potentially, no one. hence my answer:
ar-jedi |
It is almost a guaranteed certainty the government and or private broadcasting companies will have the means of transmitting radio broadcasts with news and information even if there were an EMP event. |
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I don't know about an ammo can but you can make a faraday cage. Linky |
Anyone capable of detonating a nuke 250 miles above North America would only do it as a preface to a full-out nuclear strike... And that anyone, right now, is limited to Russia and possibly China... Unless you think we'd try to nuke ourselves... Which is even more nutzo than thinking Russia or China would be stupid enough to do it... IN ANY POSSIBLE TERRORIST NUCLEAR ATTACK, IF YOU GET HIT BY EMP THE BLAST/RADIATION WILL KILL WHATEVER YOU MANAGE TO 'PROTECT' |
to Dave_A
Possible better phrase  IN ANY POSSIBLE TERRORIST NUCLEAR ATTACK, IF YOU GET HIT BY EMP, THE BLAST/RADIATION WILL KILL YOU NO MATTER WHATEVER YOU ARE ABLE TO 'PROTECT' Just my $.02 |
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If you have a metal cabinet or an old tool box, they make perfect places to store your extra electronic gear. Just make sure they are insulated from the metal of the cabinet / box. It makes no sense to leave your unused radio gear unprotected. This goes for inverters, radios, scanners, etc. John |
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The US testing in the Bikini Atoll proved the effects of EMP well beyond other effects. Farthermore while terrorists might not reach 250 mi, they could do 7 (35,000ft) which could place Washington to Boston to Ohio in line of sight from an EMP blast. BTW the trailing wire antennas did have one "burn through" function- They could access the GWEN (Ground Wave Emergency Network) repeaters designed for use after nuclear war rendered the ionsphere unusable for HF communications (and VHF and UHF are limited by LOS). The GWENs were decommisioned in the 1990s. Note the GWEN was designed for fixed site comms, but someone decided to add a transmitter to some or all of the NEACAP/TCAMO/Looking Glass aircraft. But as some one alluded to the main function was to send Emergency Action Message to naval ships, espically submarines. |
Well from the linky that "SonOfNorway" posted It says that you must have it grounded. It looks like ths guy hase done some research on it Edited to add linky |
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From the Wiki article on EMP. A high-altitude nuclear detonation produces an immediate flux of gamma rays from the nuclear reactions within the device. These photons in turn produce high energy free electrons by Compton scattering at altitudes between (roughly) 20 and 40 km. These electrons are then trapped in the Earth's magnetic field, giving rise to an oscillating electric current. This current is asymmetric in general and gives rise to a rapidly rising radiated electromagnetic field called an electromagnetic pulse (EMP). Because the electrons are trapped essentially simultaneously, a very large electromagnetic source radiates coherently. The pulse can easily span continent-sized areas, and this radiation can affect systems on land, sea, and air. The first recorded EMP incident accompanied a high-altitude nuclear test over the South Pacific and resulted in power system failures as far away as Hawaii. A large device detonated at 400–500 km (250 to 312 miles) over Kansas would affect all of CONUS. The signal from such an event extends to the visual horizon as seen from the burst point. For what it is worth, apparently for low altitude bursts, the gamma rays are absorbed by the atmosphere and produce very little EMP. As posted, EMP from normal nuclear warhead detonations is less dangerous than the radiation flash and the overpressure wave. EMP could be caused by a missile warhead fired from a merchant ship or submarine near the coast if it gets above 100 km. Not exactly high tech these days. RS |
the author of that linked info doesn't know what he is talking about.
unless "done some research" = a masters degree in electrical engineering, then i think we are not on equal footing. ar-jedi |
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Hey AR I know I could do the same thing using that copper tape (great stuff) to seal an ammo can, but I think work would miss it hinking __________________ <---lid ||+---- ||| <---angle ||| | | | | | Aviator |
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No need to ground an enclosure. Ask any one who has had a basic emag class. On two thing are required. 1)The surface be perfectly closed 2)The surface is perfectly conducting. #2 is no big deal. If you want to get 60dB attenuation (one millionth), almost anything strong enough to support itself will work. For 20-30 dB (one hundredth to a thousandth), even foil can be used (I have seen a measured loss of over 30 dB in a room covered with copper foil covered printed circuit boards) #1 is more of an issue. A door needs to be atached on all sides, a good connection at the hinge, or a ground strap won't cut it. Small hole, a fraction of a wavelength are OK, but a slit can be a killer (Because the currents flow through the opening and on the inside of the surface as they flow around the hole. The radio wave don't actually leak through the hole.) Screen is OK (resistance is an issue), Perf plate is better, best is a sort of honeycomb structure with some depth to it. I see two issues with your drawing. One the angle has to touch the bare conductive metal of the lid, and two it can't be aluminum (which builds up a non conductive oxide layer). The angle must touch so that currents can pass from the right side, through the lid, and on to the left side. It's not like blocking light. Otherwise current can start flowing on the side in such a way that they produce electric and magnetic fields inside the box. A quality attempt at this would plate the lid with something rust resistant (Zinc chromate, nickel, etc, and use a wire mesh gasket, or phosphor bronze spring atached to the angle. This is how lots of quality radios are build, and even EMP shielded rooms. BTW FEMA did some test and found you could pretty well EMP proof radios by using NEMP rated protectors on all Rf, audio, and control lines and putting the radios in a standard shielded metal cabnet rack (doors with the type of gasket mentioned.) Note FEMA's stuff is better (I've been in one of the Fema FRCs, and some of their other facilities, but they thought this was good enough for large city EMAa and state EOCs. Now, what is required to protect a non operating device- not very much. It's also hard to figure out the design basis (there may be some clasified data), but a high altitude pulse is very broadbanded (below Am radio to above microwave), while a ground burst will have all of its VHF and higher frequencies limited by line of sight. Measuring the protection of the enclosure at any particular frequency is easy. Most EMP shelters are tested at several frequencies, I forgot the standard ones, but it might be (for example) 100 KHz, 1 Mhz, 100 MHz, 1 GHz. You place the current on the walls of the room (usuall across diagional oposite corners and read the level inside the enclosure with a reciever (Spec-An) |
i see some art there, Picasso!  actually, you are thinking along the right lines, but it will be tough to do. every gap will create a slot antenna -- even with seemingly intimate contact between two metal surfaces that have been painted before assembly. so even though you have made a labyrinth for the RF, it will still couple to the inside of the box. ideally, all seams must be continuous otherwise the enclosure will perfrom poorly (i.e. will leak RF) at high frequencies. and when i say continuous, i mean continuous. one "cheap" way to do shielding is to pick up EMI gasketing wherever you can. most equipment designed for telecom or military applications will have an abundance of beryllium copper finger stock, conductive gasketing (mesh covered and/or carbon-nickel impregnated), and honeycomb waveguide-beyond-cutoff panels. the trouble with using this material on something like an ammo can is threefold: (1) you have to get the contact surfaces totally clean and free from oil, oxidation, etc, (2) you have to maintain good (high) contact pressure over the life of the enclosure for continued low resistance at high frequencies, and (3) the union of dissimilar metals (e.g. the steel lid and the beryllium copper gasketing) causes galvanic corrosion -- leading to high contact resistance. summary: it's not easy to get and keep high EM/RF attenuation. i wish i could tell you to go buy ACME brand galvanized steel garbage cans w/lids, and you will get 100dB of attenuation from DC to 50GHz for the life of the can -- but it doesn't work like that. ar-jedi   --- ps: here is a "lightweight" general purpose enclosure... www.equiptoelec.com/rfi.htm 
here is another from the same company... www.equiptoelec.com/seismicRFI.htm 
---- finally, here is an "ammo box"-sized enclosure which is definitely EMP-proof: www.emi-test-enclosures.com/power/ramsey/test%2Denclosures/ste5100-test-enclosure.asp  |
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AR Jedi is right on needing high contact pressure, but this is one of two things the ammo can has going for it, the other being the construction of a 5 sided continious box (I think, but am not sure, from one piece of steel) Since I mentioned putting operating radios in an enclosure, and Mr Jedi posted pics, it should be noted that in this case you must ground the enclosure, #1 for electrical safety, and #2 as soon as you install protectors on control/power/audio/RF lines, you really really need a ground to get the energy back into earth. BTW, the protectors I've used on RF lines are Polyphaser ISO-NEMP. Cost is about $70. They will handle everything I've worked with except satellites that need a higher frequency unit. I can't remember if they pass DC either (for an antenna tuner or active antenna, or sat phone dish). Similar protectors are used on power and audio. Also, while I do this for a living (telecom), and I do use ISO NEMPs on my ham radios, I've never bother with EMP shielding, even though I could get a cabnet one step down from the one pictured for free. We throw out a few each year. The risk to powered down equipment is low, and to equipment not conected to an antenna, power, or phone line minimal. One last thought- If you are going to put operating radios in an enclosure, running the cabling to the antenna, and power in rigid conduit will have a noticable effect of the energy hitting the protector. So will adding protectors at the entenna, and grounding the shield of the coax where it comes in the building. |
ar-jedi said:
Yep, kinda figured that, but as I say I was looking at something done on the cheap. We use lots of that stuf in the avionics industry too.
A garbage can, now there's an idea...with the round opening around the lid it should block all but circularly polarized signals..........just kidding. hanks Aviator |
stand by the trash bin and wait for someone to throw away a decent size avionics enclosure. the more screws that are holding it together, the better. the closer together the screws are, the better. the more EMI/RF gasketing seen when you do get it apart, the better. ar-jedi |