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IPFS News Link • Surviving the Collapse

Amazing Affordable Force Multipliers - Part 2, by Tupreco

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EMP-Proof Your Radio Comms With a USGI Ammo Can Inexpensively

How can you EMP-proof select comm gear for under $100? You can do this more easily than you might think. Radio comms are radio-based systems that can communicate across distances from a few miles up to thousands of miles, under the right atmospheric conditions. In order of range (and cost) these radio comms include walkie talkies using the Family Radio Service (FRS) and the General Mobile Radio Service (GMRS). Next, at higher cost and more range, is citizens band radio or CB. At the top end in price and range is Amateur Radio, fondly known as Ham radio. Be aware that all cell-based devices, like cell phones and tablets, are also radio comm systems, but they all rely completely on third parties that are under government regulation to keep the system operational. For that reason we will limit ourselves to direct two-way radio issues only.

The rugged storage capabilities provided by USGI metal ammo cans are obvious. But an amazing non-obvious feature is their ability to act as a shielding enclosure to protect your sensitive comm and other sensitive electronics from an EMP event. Large-scale high energy atmospheric transients can come from a solar coronal mass ejection (CME) striking earth's atmosphere or a strong electromagnetic pulse (EMP) from a localized EMP device or a nuclear detonation. Regardless the source, the effect is that the same potential for damage exists when power lines or antennas convert these high-energy fields into current flow through the attached wires or other conductors. The result is significant damage to connected circuit components that are unable to withstand the overload. This can all take place in a few milliseconds.

Fortunately, an electrically conductive solid metal box like an ammo can has an inherent property called the Faraday cage effect that can shield its contents from large external transients. Michael Faraday realized in 1836 that an electrostatic electric field would not penetrate a metal enclosure. Later it was determined that same effect prevents penetration from other energy fields such as electric, magnetic or radio frequency. The Faraday cage works because the traveling energy field transforms into an induced voltage and current flow across the surface of the conductor (in this case the metal box) to ground or eventually dissipates into the surrounding area without affecting the contents of our box which is now our Faraday cage. Secondary grounding is not essential. However, make sure no conductor like a power cord or antenna is connected through or penetrates the enclosure or all shielding bets are off. Those penetrating conductors will act as an antenna also and expose the contents to unwanted energy spikes. To clarify your own understanding of EMP and RF shielding I direct you to Don White's excellent book on the subject.

To implement this idea, put your radio gear or other sensitive electronics inside the box and make sure it is closed tightly. Making sure the top and bottom are electrically connected with an ohm meter is a nice for peace of mind. Ammo cans usually contain a rubber seal between top and bottom but connect electrically through the hinge pins. You may want to attach a small gauge lead as a redundancy between the top and bottom. A decent alternative to an ammo can would be to use a large zip style static shielding bag that is kept tightly closed. The zip close style sized for a 5-gallon bucket would be a good choice. If you use such a bag, then the outside box composition doesn't matter, because the conductive foil layer inside the bag is the actual Faraday cage.


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