Hello Jim –
Fantastic Blog – I am a little late to the party and just discovered SurvivalBlog last week working some survival related searches on Google. I read your novel [“Patriots”] too, years ago, and thoroughly enjoyed it.
My questions: I have searched around and can not find much practical information on Faraday Cages, especially directions for constructing them at home. What design is effective? What is not? Should they be grounded? etc. I know this information is out there, and I’ll bet that more than one reader of the Blog can help – and I’ll also bet that the topic will interest most readers. Also, there seems to be a renewed interest in radiology survey equipment in general – check out eBay for the recent flurry of activity of sellers with the old 1960s Civil Defense survey meters, dosimeters, and dosimeter chargers…thank you Iran and North Korea! I know that some older transistor-based radios are thought to be very resistant to EMP, I was wondering how these vintage instruments would hold up. Thank you. – Rowland
JWR Replies: I’m not an RF engineer, so don’t take the following as gospel, but I did do some research on EMP, as background for a series of EMP hardening and test articles that I wrote for Defense Electronics magazine back in the late 1980s. For that series, I took a trip to Kirtland Air Force Base, New Mexico where I interviewed a half dozen EMP specialist engineers and toured the U.S. Air Force TRESTLE facility.
My general advice for those that suggest making their entire house into a Faraday cage: Don’t. It will probably be wasted effort. The biggest problem is that any external linear metallic structure such as a radio or television antenna, a phone line, or a power line that enters the house will act as an EMP conductor and make the cage useless. Second, unless you are quite meticulous about making the cage a completely integral shell without any gaps, then it will allow the passage of the pulse. (I can’t imagine the complexity of building an entirely off-grid house with no outside communication, no external antennas, and all power generation done inside of the Faraday cage!) Second, every window screen must be grounded to the rest of the house “cage” and every door must have interlocking “teeth” around its perimeter. Even the floors must include a mesh. Lastly, the often cited but fallacious “one inch mesh chicken wire” approach is insufficient, since EMP waveforms are very broadband, and include some very short wavelengths. Unless the mesh apertures are smaller than the shortest wavelength of a pulse, then the mesh will leak. IMHO, you are much better off storing spare disconnected radios, computers, and automobile electronic ignition components wrapped in aluminum foil and/or stored in steel ammo cans. This approach is essentially foolproof, and less expensive in the long run. A side benefit is that it will also provide spare/redundant electronics for other non-EMP disaster situations.
Any corrections, differing opinions, or suggestions on large scale Faraday cage construction, folks? (I appreciate your counsel. 12,000 heads are better than one!)
As for Civil Defense rate/survey meters: Any meters from the early 1960s (which is when most of them were made) will have have discrete transistor technology that should be immune to all but the most intense and localized EMP. (Read: If they were affected, then you’d be inside the blast radius and would probably killed instantly.) It is only later microcircuit (“chip”) technology that is vulnerable to EMP. In general, the smaller the gate size, the more vulnerable a microcircuit is to EMP. (Hence, the latest chips with sub-micron dimension gates are quite vulnerable.) In the event of EMP, you can kiss your Pentium chip PC goodbye.