KNW-131 Protecting from EMP


Edited 09/2022 by Paul Smith, K5PRS
Revised 12/2021

As amateur radio operators, we try to be prepared to assist in all types of emergencies however there are two emergencies which are more difficult to be prepared for: they are a high intensity flare from a Solar Storm (EMP) or a High Altitude Electromagnetic Pulse (HEMP) from a high-altitude nuclear explosion.

The last Solar Storm that creating significant damage occurred in 1859. It was so powerful that it destroyed major sections of electrical wiring, light bulbs, telegraph keys and other components as it energized telegraph lines to the point of burning up infrastructure and sending severe shock through key operators in the Northern Hemisphere. A storm of that magnitude today would have a much greater impact on today’s grid connected and highly sensitive integrated circuit components.

A high-altitude (above 30 miles) nuclear explosion above the central US could completely wipe out electronic systems thousands of miles away without causing any human casualty. It is estimated that 6 or more states would be affected. A detonation at 300 miles would take out the entire US. A moderate strength (yield) detonation is capable of producing field amplitudes of up to 50,000 volts per meter at ground levels over a diameter of thousands of miles away from the explosion.

A detonation can have various effects on radio communication including burning out equipment components due to the intense transient voltages that are generated. Operators many miles from a detonation could experience power blackouts, signal absorption or abnormal reflections due to effect in the ionosphere plus increased noise or phase distortion. The atmospheric effects just described will dissipate over time but the damage to your equipment from transient voltage surges could be permanent.

Equipment can be “hardened” by protecting sensitive circuits against the high voltage or current spikes. However, RF shielding of all your equipment may not be practical. Vacuum tube systems or backup equipment that has been stored disconnected from power and antennas may be useful. Research Farraday Cages for more information on proper storage. Knowledge is the first step towards solving this problem.

Simulated testing of various manufactures of amateur radio equipment in 1986 demonstrated that most amateur radio equipment should be protected from EMP as long as the following conditions exist:

  • Long external wires are not attached. Short wires such as microphone and power cord did not cause a problem if the power cord is not plugged into the grid.
  • If power lines or antennas are connected, then adequate transient-pulse protection must be placed in these lines.

Dennis Bodson, W4PWF, gave the following suggestions in a series of 1986 QST articles:

  1. “If you have spare equipment, keep it disconnected; use only the primary station gear. The spare equipment would then be available after an EMP event.
  2. Keep equipment turned off and antenna and power lines disconnected when the equipment is not in use.
  3. Connect only the external conductors necessary for the current mode of operation.
  4. Tie all fixed equipment to a single point earth ground to prevent closed loops through the ground.
  5. Obtain schematic diagrams of your equipment, tools, and components for repair of the equipment.
  6. Have spare parts on hand for sensitive components of the radio equipment and antenna system.
  7. Learn how to repair or replace the sensitive components of the radio equipment.
  8. Use nonmetallic guy lines and antenna structural parts where possible.
  9. Obtain an emergency power source and operate from it during period of increased world political tension. The power source should be completely isolated from the commercial power lines.
  10. Equipment power cords should be disconnected when the gear is idle. Or, the circuit breaker for the line feeding the equipment should be kept in the off position when the station is off the air.
  11. Disconnect the antenna lead-in when the station is off the air or use a grounding antenna switch and keep it in the GROUND position when the equipment is not in use. This is also good practice to protect against lightning strikes.
  12. Have a spare antenna and transmission line on hand to replace a damaged antenna system.
  13. Install EMP surge arrestors and filters on all primary conductors attached to equipment and antenna.
  14. Retain tube type equipment and spare components; keep them in good working order.
  15. Do not rely on a microprocessor to control the station after an EMP event. Be able to operate without microprocessor control.”

(ref. ARRL QST Magazine of Oct, 1986, p38-41)

To update this information 20+ years later, we need to realize that more of our current day amateur radio equipment has remote microphones, speakers and remote/separable heads all of which generally have electronic controls, amplifiers, etc. in molded plastic shells and often connected by lengthy cables. Protecting your gear takes planning and advanced preparation. Unprepared, a HEMP launched from a submarine or container ship just off our shores could take you out of the radio game before you have an opportunity to react…permanently. Make sure at least one complete system is tucked away and well protected. Having an equally well protected solar power system or EMP protected generator is another important consideration. Remember that generators are only good so long as the fuel supply lasts. EMP events are not short term events. Even if you can replace the gear and get back on the air, it will be long after the disaster is over and long after your skills and abilities are needed.

There are inexpensive ways to protect (some of) your gear:

One is simply to use an all metal garbage can with a tight fitting lid to store your spare equipment. Some recommend that equipment needs to be insulated from the inside of the Faraday cage. That is good insurance. Use cardboard or foam strips for this. The cage MUST NOT be grounded. If you keep the garbage can on a concrete floor, make sure it sits on a layer of insulation. Run a strip of conducting tape around the lid to ensure that the seam is well protected.

For small pieces that you might want to access from time to time (not recommended), use EMP bags. There are several options on the market. These bags consist of Mylar that has two layers of metal alloy (aluminum) built into it and a plastic lining to insulate your equipment. The Ziploc closure or closing clamp makes it easy to use and reuse the bags. These bags could be used to store your standby go kit equipment but in the unlikely event you are using the equipment when an attack occurs you’ll be out of business. They are also waterproof which is a plus.

For larger equipment like generators with electronic components and solar generator components, build a plywood box (insulation) and cover it with metal sheets. Solder (or weld) all seams and run conductive tape along door seams. As above, insulate from the ground. Small pieces of electronic equipment can be stored in cheaper, but still waterproof, zip closure bags along with the large equipment.

Here is a list of other items you may also want to consider protecting:

  • Laptop computer
  • AM/FM radios
  • Television/Blue Ray & CD players
  • Cell phones
  • GPS devices
  • Calculators
  • Electronic clocks
  • Battery chargers
  • Electronic tuners
  • Power Inverters
  • Anything with an electronic ignition (some chain saws, generators that use electronic ignition, electric bicycles/scooters/motorcycles)
  • Kitchen appliances
  • Hard drives, thumb drive and other electronic storage medium

When you consider the above list, keep in mind that it might be a very long time before power is restored and you’d need two of everything to get the job done.

There are several recent articles and videos on the internet about this subject which you can research. I have tried to boil the subject down to the minimum essential information for training and awareness. To test if your Faraday cage container is working, place your cell phone in the container and try to call it from another phone. If it does not ring then your container is working. Another method is to put a transistor radio blaring a strong local station in the container. If you can’t hear the music, the Faraday Cage is working.

That concludes tonight’s training. Are there any questions, comments or suggested additions?

Thanks, this is (callsign) clear to net control.