In a comment to yesterday’s post, Robert Hewes asks if my radios are stored in a faraday cage. I assume that he is asking the question because he has heard of EMP, or electromagnetic pulse, and its ability to damage solid state electronics. I will explain why this should not be a concern for most preppers.
EMP works by exposing semiconductor components to voltages high enough to break down the semicondictor. There is nothing magic about EMP, it is simply a powerful radio wave in the microwave spectrum (4-20 GHz) with a wavelength between 1 and 5 centimeters. This pulse is subject to the same physical laws as any other form of electromagnetic energy. The two that you have to keep in mind are the fact that radio waves travel in straight lines, and that their energy dissipates according to the inverse square law.
EM energy traveling in a straight line prevents it from damaging anything beyond the horizon, and the inverse square laws say that energy drops off that the inverse square of the distance. An EM weapon capable of damaging electronics at half a mile would require 250 times as much energy at 60 miles.
To extend the reach of an EM weapon, you must either set it off relatively high in the atmosphere, thus extending the horizon, and you must greatly increase the power. Weapons that cause long range EM effects to semiconductors over great distances require a lot of energy. This is why nuclear weapons produce the powerful pulses that reach long distances, but not many others.
Couple that with the fact that radio equipment is hardened to withstand certain amounts of EM, due to their nature (they are built to receive EM, after all, they ARE radios, it’s kind of what they do), and the problem becomes even more difficult.
In short, I am not worried about it. There are many things that I can prep for, and EMP is not on the radar.


Robert Hewes · April 23, 2012 at 4:38 pm

That makes sense — I guess it's a cost/benefits calculation, right? Thanks!

Divemedic · April 23, 2012 at 8:46 pm

Sort of. I figure that me using the radios on a daily basis gives me more benefit than the slight risk of being within the effective range of an EMP weapon. By networking with others, and becoming familiar with the equipment and its limitations, I am enhancing my preparedness more than I would by leaving them locked up in a Faraday cage.

SiGraybeard · April 27, 2012 at 3:21 am

The standard mathematical EMP models I've seen are somewhat different from what you describe. They describe it as a very short pulse of about 50,000 Volts, peaking by 5 nanoseconds and pretty much over by 100 nsec. It's similar to lightning in voltage, but a faster.

When you do an FFT of that, the majority of the power is under 100MHz, and I can't see much making it to the microwave spectrum.

While EMP will wreak havoc on the power grid and phone lines, it's not going to knock planes out of the sky and it's not going to destroy things just sitting on a table (not plugged in). I've seen tests with simulated EMPs where cars are shut down, but simply turning the key starts them back up. The ham magazines have printed tests, too, and small VHF/UHF handhelds were not damaged. Bigger radios were ok if they were not connected to big antennas. It seems if the problem is broadband energy the EMP creates, filters to reject that energy are your first and best defense. Metal boxes were not required.

Balance this all against the fact that a continent-sized EMP has simply not been observed and you always have to wonder how good the models are…

Divemedic · May 4, 2012 at 12:42 pm

It depends. A nuclear weapon generates EMP in the 1kHz to 100 MHz range. A pulsed EMP weapon uses high powered microwaves, which are far more damaging, but have much less effective range.
I chose to look at EMP weapons, since a nuclear exchange would create far more things for me to worry about than the fact that my HAM radio isn't working.
Nuclear effects:

HMP effects:

Comments are closed.