That was previously published HERE on ModernSurvivalOnline.com. From some recent correspondence with the Panhandle Rancher. Published with his permission. Thanks Panhandle!!
I performed a biennial check of H/T’s and marine VHF base units stored in the family bunker the other day and am enclosing a couple of photos of how they are EMP shielded (double ammo boxed, insulated inside the first box and outside with cardboard and metallic taped. I metallic tape all seams and weld points on the ammo boxes. Big electronics are stored in original packaging inside ammo boxes and smaller H/Ts are first packaged in foam bags wrapped in aluminum foil that in turn is wrapped in cardboard). I also have solar charge controllers, a FLUKE DVM, LED flashlights, NVGs, range finding Leica binoculars, NICAD and DEWALT battery chargers, several battery/solar powered scientific calculators, a 100W multi band amateur radio, and 150W Marine HF transceiver thusly protected. I back fill all containers with N2 gas before sealing. As the humidity is quite low in this region, I don’t use silica gel.
Some similarly protected electronics sealed in multiple 20mm ammo boxes are also metallic taped, insulated, and stored inside US Military aluminum medical chests for additional shielding. The large medical chests are placed on wood planks in CONEX containers for more protection and I plan to build a metal frame/aluminum skinned building around two of the containers, thus adding another layer of shielding. A John Deere diesel (no computer) M-Gator and spares will be stored in one of the CONEX containers and the other will be filled with force multiplying electronics including unused solar panels and GRUNDFOS water pumps. I’m thinking of throwing in several Apple laptop computers and a printer or two with supplies as well. Elsewhere I have a half dozen best office quality manual typewriters, spare ribbons, and reams of paper. I suppose I should throw in a couple of coils and ignition wiring for my 1974 Jeep we call TEOTEAWKI. Several one ton ranch trucks are older 4wd diesels. I cut down a JD wheat drill and disc into 5′ long units so they could be pulled behind a horse, the Jeep, or the M Gator. Will send you photos of these if you are interested. Not much way one could harness a team to pull a 20′ disc or drill.
If you think of anything I’m missing either in EMP protection or stores, please let me know.
– Panhandle Rancher
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Very nice, concise article. I have a question though, I have read that sometimes people will pull out the rubber gasket on the large ammo cans and replace it with a metallic mesh rolled up and put into the same place to ensure good contact. I have also read that some people will take their ammo cans and then place them in a container with a copper mesh around it to ensure good connectivity. How far do you really have to go with the layer after layer of shielding and what is too much?
One of the wonderful things about US military ammunition boxes is their waterproof qualities. This has value in protecting electronics. Use of the metallic duct tape around the lid should obviate the need to remove gaskets. The more insulated ‘nests’ of metal boxes the better as one will never know in advance the strength of the EMP pulse. Not believing in half way measures, some of my deep stores, especially force enhancing items such as radios and night vision are protected behind three metal barriers and thence inside a Continental Express (Conex) shipping container. Of course a few such are in discrete buried cache.
I once supervised a facility that provided TEMPEST standards testing and evaluation. There are a lot of differences between electromagnetic intelligence bearing signal leakage and EMP but many of the protective features are identical. The shielded rooms were continuous metal with a vault like door. The door perimeter had copper ‘fingers’ that meshed with those of the frame. Power was highly filtered and communications were optically isolated. Other than the power filter which may be inadequate to stop high power EMP, the other protective features are directly applicable.
Wavelength decreases with frequency. Smaller voids in shielding increase attenuation of high frequency electromagnetic radiation, hence my use of metallic tape thus reducing the void between lid and container to the thickness of paint and tape adhesive. Multiple nested and electrically isolated similar enclosures would serve to greatly attenuate any EMP including conventional electromagnetic radiation, however please do not confuse attenuation of radio frequency electromagnetic radiation with EMP protection. Having so said, I would suppose that a vehicle inside a red metal building such as most airplane hangers (which typically have no windows only a sliding door and metal entry door) would have a greater chance of surviving an EMP event than one setting outside.
When it comes to EMP, the more isolated barriers the better with attenuation increasing behind each barrier.
I have been looking for so long for info like this. Thank you for such detail and photos. I wonder if you might have the answer to a few other questions that I’ve had? I would like to know if the following things need to be shielded or if they would likely be fine…a 30 year old TroyBuilt tiller with a pull string start, or an old (1950) Johnny Popper? thanks so much.
Just a reminder–those containers need to be grounded to truly be effective so any electromagnetic energy gets shunted to ground. You can readily see why this is important by doing this experiment; Take two UHF HTs, turn them on and wrap one with aluminum foil. Now transmit from the unwrapped and you will notice the other still receives just fine. Why? Shielding alone won’t stop electromagnetic energy–it must shunt or carry that energy straight to ground to be effective. Now ground the foil and any reception will stop. The above practice can work but may not if all metal surfaces are not also bonded (i.e. electrically connected to each other–think container and lid). The tape may do this but, it may not.
PR, it’s your equipment. Grounding keeps the various pieces from capacitively coupling to each other and instead makes that coupling to ground. I should have been clear–what you’re doing will work very well and should be good for 80-100db of attenuation (which is needed for EMP protection). But, if there’s any weakness (i.e. your lid manages to be electrically isolated from the container), grounding (and bonding) will help shunt the energy and save things.
It would be very hard to ground multiple nested containers without obviating the advantages of nesting isolation. There are many many manufacturers of portable mil spec faraday enclosures, none are grounded. See:http://www.empengineering.com/storage-faraday-boxes. Amateur radio operators know how difficult it sometimes is to obtain a satisfactory RF frequency ground. As a youth and novice back in the 60s I had trouble conceptualizing the need for a flat grounding strip or use of copper tubing (due to the skin effect at RF frequencies) instead of conventional wire. Another example of RF grounding for communications frequencies can be found at:http://www.swssec.com/grounding.html. See all of that bright copper plate? Needless to say, simply soldering a lug onto your metal box or penetrating with bolt and nut and thence to a heavy gauge copper wire is useless at RF frequencies. The TEMPEST rooms I worked with were grounded but because of isolated power supplies that passed AC mains into the inside of the container. Smaller Faraday chambers without any sort of electrical penetrations should never be grounded.
I’m traveling for work but would be happy to explain more and why but, not on a public forum. Shoot me an email and I’ll explain. I did a quick search and it turns out Art Bradley posted a good video on the dangers of even the smallest gaps on Faraday cages (like those in your tape around the latches): https://www.youtube.com/watch?v=aMct99DiZak
But, that doesn’t answer the ground question. Next post…
Try this; take two GMRS/FRS HTs and turn them on. Wrap one with aluminum foil and try to transmit to it with the other. You’ll note the radios still work. Now ground the aluminum foil and you’ll note that the radios stop working. Why? Grounding is insurance. There are no slot antennas (formed by even tiny gaps) on a ground plane–the signals get shunted to ground. I’m not saying you must ground your containers. What I’m saying is that your Faraday cage better be perfect and not have any gaps if you don’t. BTW, I use an aluminum box without EMI gaskets or latchs so I can completely tape seal the lid. And yes, it has two large bonding straps that run to my antenna tower ground system.