EMP Protection for the Radio Amateur, an Encore.

A follow up to my November 2017 article about electromagnetic pulses (EMP) was not in the plan. Then Off Grid Ham reader “Charles” hit my email inbox with a bounty of information related to this topic that was too good to keep to myself. I’ll respect his request not to be publicly identified for this article, but I want to thank him for his generous contribution of knowledge.

I’ve gone through everything Charles sent and came to the conclusion that EMP has been overlooked by the ham community to a much greater extent than originally thought. And amateur radio leadership, such as it is, has not produced or sponsored any meaningful data about EMP in over a generation!

Addressing the unknowns of a DIY Faraday cage.
As we discussed last November, home brew Faraday cages are an unknown because all the ideas out there are basically guesswork designs. None have been exposed to an actual EMP or tested in a lab for EMP shielding effectiveness. Charles’ experiments answer some of the questions.

He built a Faraday cage and also took the time to test it and document the results. In his version, he completely covered a cardboard box with an overlapping layer of aluminum foil and sealed it with metallic tape, then placed that box in another box (“nesting”) and covered it again with foil. He states that it is very important that the foil generously overlaps (3.00″ minimum) at the seams and makes good electrical contact with itself.

With a single layer aluminum covered box, he got -50 dB attenuation on a spectrum analyzer across the tested frequencies, which itself is pretty good. After adding the second shield layer he measured -80 dB attenuation or better, which meets military standards:

Container Description

Signal source

Dist. Betw. Antennas


Unshielded Signal

Shielded signal





Cardboard box, dual wall

Yaesu HT, 7” Yaesu rubber duck antenna

1 meter

146.45 MHz


Not seen- either fault or Less than -106 dBm noise floor

100% foil coverage, seams taped with 2.5” alum tape

1 meter

147.43 MHz


Not seen- either fault or Less than -106 dBm noise floor

Box top seam cut, re-taped with alum tape

1 meter

446.50 MHz




1 meter

New foil added to cover open seams, then those seams taped

1 meter

446.50 MHz




Cardboard box, dual wall, 100% foil covered, seams taped with 2.5” alum tape

1 meter

446.50 MHz




Cardboard box, dual wall, 100% foil covered, seams taped with 2.5” alum tape inside 2nd box 100% foil covered, seams taped with 2.5” alum tape

1 meter

446.0 MHz




These measurements were made on July 19 and 20, 2016 with a Signal Hound USB-SA44B spectrum analyzer and Spike software.

Charles’ testing demonstrates that the most effective EMP shield has the following qualities: 1) more than one layer/container (“nesting”), 2) make sure the layers/containers are insulated from each other, and 3) make sure none of the shields are grounded. A galvanized trash can & lid or metal file cabinet with the seams, cracks, and openings carefully sealed with metallic tape could count as one of the layers.

There is an important caveat to Charles’ findings: Although he went though a lot of careful effort to test his system accurately, and I am satisfied that he controlled for all the variables to an acceptable margin of error, his experiments were not performed under recognized test conditions and across all possible frequencies. To be clear, what Charles has done is far, far better than guessing & hoping, but it’s important to point out it wasn’t a level of research that would be done by professionals in a lab. Until the ARRL or some other group produces properly calculated data (more on that in a moment), this is as close as we’re going to get.


Charles’ home-brew EMP Faraday cage. This box alone tests at -50 dB attenuation across most frequencies. Note the generous use of metallic tape. Place this box in another aluminum-covered covered box and the attenuation goes to -80 dB. OFF GRID HAM READER SUBMITTED PHOTO ©2016

The EMP library.
Unfortunately, there are very few credible books and articles that address EMP in a way that is useful for amateur radio or off grid energy. Charles tipped me off to two, one of which hits the mark perfectly. The other falls short but can still be harvested for ideas.

EMP-Hardened Radio Communications by William Prepperdoc is well worth the money and offers real-world solutions for protecting your gear from EMP. More importantly, it describes how to protect the everyday equipment you are not storing in a Faraday cage, including your solar panels and inverters. After all, you want to use your stuff, right? You can’t hide everything in a can forever, but you don’t want to leave equipment vulnerable to EMP. Prepperdoc gives plenty of options. All of his suggestions can be implemented inexpensively and without advanced technical knowledge. He wraps up his book by discussing issues & strategies related to communicating after an EMP strike. At about $10.00 for the print version or $4.99 on download, this book is an excellent value.

The only criticisms I have are very mild ones: “William Prepperdoc” is an obvious pseudonym and this is a self-published/independent book. No specific information is given about the author’s qualifications other than stating he is “an engineer, ham, and physician” (the latter of which is impressive but has nothing to do with being an authority on EMP). Furthermore, self published/independent books are an automatic red flag. I’m not at all saying the guy doesn’t know what he’s talking about. I’m only saying there is no way to vet his qualifications and he doesn’t exactly inspire confidence in his work by being deliberately ambiguous about his professional background. The reader is left to take it on faith that Prepperdoc is a true expert.

On a related note, I am a stickler for verifying the credibility of information and the people who produce it, whether it’s for a personal project or researching an Off Grid Ham article. You should vet your sources too. It’s the internet age where anyone can appear as a very convincing “expert”.  Most have honest intentions but simply don’t know the material as well as they believe. A few are genuine experts.  The rest are willful frauds and pretenders.

The second book on the reading list has the lengthy title, EMP – Protect Family, Homes and Community: First in a Series on Nuclear Electromagnetic Pulse Protectionby Don White. I could not find any subsequent books in the series and Mr. White is now deceased, so I assume Volume One is all we’ll get.

White’s qualifications as an engineer are extensively documented. His book is more conceptual than practical and spends an inordinate amount of time discussing EMP shielding methods that the average person would have neither the skill nor the money to do (such as shielding an entire house). If you enjoy theory, statistics, geeking out with IEEE standards, and math, this book is for you. A motivated hobbyist could adapt White’s material to everyday use but it would take some patience to wade through it.

The book does offer a lot of background information that is outside the realm of amateur radio but is nonetheless useful, such as how geography effects EMP survivability and the lack of government and industry interest in addressing EMP threats.

White’s book is somewhat expensive. The print edition is about $23.00-$35.00 depending on where you buy it. I don’t think it is worth that much to the average radio amateur. I went for the downloaded electronic version on Amazon for $9.75. At that price point, it’s worth having.

White also left behind numerous very useful articles that are on line for free. Just google “Don White EMP.”

The ARRL has been totally sitting this one out.
One party that has been glaringly absent on this topic is the ARRL. The last published information about EMP produced by the ARRL is from 1986! It was presented as a four part .pdf, and three of the four parts are no longer online. Our contributing reader Charles recently contacted the ARRL and got no reply when he suggested they update their decades-old advice. His thoughtful correspondence to them reads in part:

“…my reading of articles and blog comments leads me to believe that many radio amateurs are confused about this subject and are basing their preparations on incorrect information from Internet sources or technically misinformed hams or disaster preparation sites.”

Wow, Charles sure got that one right! The ARRL has completely blown off an important subject about which many radio amateurs are seeking guidance. Having no other options, hams must fend for themselves with unverified & untested methods. It is both surprising and disappointing that the premier organization for amateur radio in the world has said nothing about EMP since long before the internet was as common as indoor plumbing and microprocessor electronics creeped into every detail of our lives.

I’m hoping somebody in the ARRL executive suite reads this article and takes action to give radio amateurs something to work with besides a 32 year old document that is missing 75% of the original text. In the meantime, if the ARRL’s excuse is that they didn’t know anyone cared, then the radio amateur community can easily fix that misunderstanding via emails, letters to the editor, online forums, and on air conversations.

What you need to know.
I am deeply grateful to Charles for coming forward to share his important experiments, insights, and book recommendations. Through this kind of collaboration and spirit of service, we can advance the amateur radio avocation.

The topic of EMP is not nearly as glorious or fun as other aspects of amateur radio but I urge hams to take measures against this very real threat even if the methods are of unknown effectiveness. We also need to pressure the ARRL to catch up with the times and provide meaningful, credible data that hams can use.

17 thoughts on “EMP Protection for the Radio Amateur, an Encore.

  1. Mike, KEØGZT

    Thanks, Chris. I will contact ARRL within the next week. Hopefully others will do likewise. I will also make mention of it in my blog. Your update is much appreciated. Thanks to ‘Charles’ as well! As an ARRL member, I too think this information is important, and deserves attention.

    1. Chris Warren Post author

      Thanks for your follow through, Mike. By the way, for everyone else, you don’t have to be an ARRL member to speak up.

  2. Robbie

    I know the ARRL has some info on EMP, There’s not near enough people in that organization or preppers that are paying much attention to it. They seem to worry more about their weapons, ammunition and food storage and put radio communication along with EMP at the bottom of their list.

    1. Chris Warren Post author

      If the ARRL has something on EMP other than the article from 1986 that I dug up, I’d sure like to know where they are hiding it.

  3. randall krippner

    Thanks a lot for the follow up on EMP. And please convey my thanks to Charles as well. It’s people like him who are willing to go through all of the work, testing, data collection and other necessary tasks in order to get real answers who keep science moving forward.

    — As for the ARRL, well one should remember that in the grand scheme of things it is a fairly small organization that is stretched pretty thin these days. It can’t be all things to all people, as the saying goes. While you, I and the readers of your blog are interested in ways of protecting equipment from EMP, I suspect the average QST reader would rather see that space go to a product review. When they publish an article in QST or publish a book, that item has to generate enough interest from the magazines readers or, in the case of a book, sell well enough to at least cover the costs of the research and publishing. That means it has to have the widest possible appeal to potential readers or there will be hell to pay when the board of directors meets the next time. This is why people like you and Charles, people who are willing to devote the time, resources, knowledge and money to do the actual experimentation, data gathering, develop the technical expertise in areas that aren’t popular enough for ARRL to deal with, are so important.

    1. Chris Warren Post author

      I understand that the ARRL can’t address each and every issue to the satisfaction of all. Still, way back in 1986 they thought EMP was important enough to issue guidance, and it’s a much more relevant topic now than it was then. I can’t accept that EMP is “not important enough” to merit attention. Randall, I appreciate your contributions to this website and I always enjoy your comments and insights. Thanks, and 73.

      1. randall krippner

        Hi Chris. I had some time this morning and did some digging around and wow, you are absolutely right, there is so little real information out there about protecting devices from EMP that it’s ridiculous. I did find one item that might be marginally useful to some people, an article about protecting diesel generators from EMP at https://www.engineeringresearch.org/index.php/GJRE/article/view/1587/1518 It’s intended for larger backup generators, but some of the techniques they talk about might be adaptable for use in other areas.

        — Unfortunately, aside from that one item, almost half an hour of digging and sorting through various references resulted in pretty much nothing about actual tested procedures for protecting equipment. Most of what I found referred to the electrical grid as a whole. Several ARES sites offered the ever helpful advice of “put your equipment in an EMP proof container”. Real helpful, that one.

        1. Chris Warren Post author

          Well it seems you have seen for yourself what my own investigating has concluded: There isn’t a lot of definitive EMP data out there, and what is out there is not very useful to radio amateurs. So I’ll go back to Charles’ original proposal and that is to lean on the ARRL to address this issue. I doubt they will act just because I say so, but hopefully they will hear from enough hams to make a difference.

  4. John Breland

    I have a few thoughts to discuss. It appears to me that when covering boxes with foil, the main issues are proper overlap of the foil seams and being careful to properly seal the corners of the box.

    Could these issues be addressed by using a round cardboard tube instead of a square box? If you used a cardboard tube like is commonly used for concrete forms, you would eliminate the seams except for the ends. Attaching foil to the inside might become a challenge, but spray adhesive and a smaller tube to press or roll the foil to the inside of the form should work. I also imagined a large expandable balloon of some kind might press the foil against the inside of the form.

    I also have a question about seams. You only mentioned overlap. Is there any advantage to folding both ends of the foil so they overlap each other in a “Z” pattern as opposed to simply overlapping them? I’m imagining the type of seam that is used to build HVAC vents.

    Back to the tubes for a moment: Could there be any advantage to creating a “loose” foil connection on the ends? This is hard to put into words, but think about how a package of Jiffy-Pop popcorn would expand as the popcorn expands. Could this possibly be superior to a “tight” foil seam on the ends?

    Thanks for the very thought-provoking article.

    1. John Breland

      As an edit to the above article:
      1) I should have written: “eliminate the CORNERS except for the ends”. My concern with the corners of a box is that this could be a substantial location of openings in the foil caused by abrasion. Pehaps an extra layer of adhesive foil tape on the corners could help with this? Any comments about using another type of tape to help with the abrasion issue like duct tape fiberglass strapping tape?
      2) When I wrote about using spray adhesive, I ommited that I believe it should be used on All surfaces to firmly attatch the foil to the cardboard.

    2. Chris Warren Post author

      John, thanks for your comment. As I mentioned in my article, there isn’t a lot of documented research to go on, so it’s not clear what really “works” and what doesn’t.

      As for your suggestions, I think it would not matter whether the foil is loose or tight or by what method it is attached, or even the shape of the container, as long as there was continuous coverage over the entire container. Likewise, it’s probably ok to add duct tape or other reinforcement to the chafe point providing the integrity of the underlying shielding material is maintained.

      Your questions bring up the importance of having the ARRL or some authoritative body update the research so we don’t have to guess.

      Thanks again for your comment. I hope you’ll stop by Off Grid Ham again soon.

  5. OhMyBet

    Most all ARES members are volunteers associated with ARRL yet we get nothing from them. Not even window stickers! ARES is a plus for ARRL and the teams need support to keep membership. May I suggest a price cut for items in the store for ARES items I.e. hats, clothing, stickers and etc. I would think you would want team members to advertise for you.

  6. Gordon KX4Z. NCS521

    I think you will find that the Pepperdoc fellow knows his stuff pretty well. The point He is making is that Faraday cages are quite limited—when would you ever be willing to take your gear out after the first flash? Couldn’t there be a second attack?

    The early 1980s articles in QST were obviously a government plant in an attempt to raise amateur radio preparedness and awareness. Having gear that could actually survive an EMP attack while in operation isnt that hard to accomplish. Pepperdoc appears to have been trying to get people to go that direction ….

  7. Gordon KX4Z. NCS521

    All 4 parts of the QST article can be read here: http://qsl.net/kx4z/QST-Electromagnetic_Pulse_and_the_Radio_Amateur.pdf

    Like almost all other research in this area, it was done with EMP simulators. There are many people who can set off a nuclear bomb in the upper atmosphere at will to test their protection systems.

    However, the spectral components of a high altitude EMP are fairly well-known, there are mil spec standards for what your equipment must tolerate, and even in the 80s, quite a few pieces of gear survived quite well. You might note the number of references in books that you read; the books with the documented references are the ones to trust.

    1. Chris Warren Post author

      Hi Gordon, thanks for your input.

      You are right that the number of references and footnotes in a book says a lot about its credibility (more is better). Another good measure is how much a given author or book is cited elsewhere, and by “cited” I mean in actual scientific research, not obscure blogs and Internet forums. Google Scholar is a good tool for this purpose.

      Thanks again for your feedback. I hope you’ll come by again soon.

  8. Gordon KX4Z. NCS521

    OOPS, Siri typo. Meant to say there are not many people who can perform a nuclear explosion to test their systems. Sorry, didn’t catch that one before hitting the send button.

  9. Gordon KX4Z NCS521

    There are more and more systems being marketed with claims of EMP hardening to one degree or another. With mil-spec’s in existence, companies with $$$$ can simply design to the spec. Ham radio operators….not so much. But EMP is little more than an ENORMOUS case of normal RFI. Filter out what you don’t need for communication; voltage clamp the rest; shield what you can; keep backup gear in Faraday cages.

    I’ve seen the PrepperDoc fellow cited in “For official use only” briefings within the DHS SHARES system…. Military is already far down the road of EMP-preparedness….hams far far less. The QST articles give huge amount of information.


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