Monday, June 3, 2013

On EMP and lightning protection

One of the things that we as preppers have to be prepared to deal with is a loss of communications. One of the ways that I have dealt with this is through HAM radio. There were some questions about my HAM radio setup and EMP protection when I posted about it last year. Now that I am back in my house, I have more options for making my radio systems a bit more hardened to EMP. Being that I live in the center of Florida, the lightning capitol of the world, this is a wise idea.
Some facts:

(If I am mistaken on any of this, there are some readers who are more knowledgeable than I, and they can feel free to correct me in comments.)
Lightning is an electromagnetic pulse that is pretty powerful, delivering an average of 18,000 amps to whatever it strikes. A lightning strike typically contains 2-5 pulses of electricity. The first pulse is called the leader, and it breaks down the resistance of the air as it heats it to 50,000 degrees F, changing it into a plasma state. This leader channel allows 3-4 more pulses to follow at 50 millisecond intervals. This is the reason why lightning seems to flicker.
The rapid rise of power with each pulse generates radio frequency energy at frequencies ranging from 20 kHz to 15 mHz. Unfortunately, this is the area where much HAM equipment operates, and it is thus vulnerable.
Where I live, we have an average of over 90 thunderstorm days a year. In my area, a 50 foot radio antenna will be struck an average of twice per year. This is why I have upgraded my EMP protection.


I spent the weekend driving copper ground rods. 6 of them in all. There are three, 8 foot copper ground rods just outside of the room that I am using as a radio shack. They are in a triangle, and spaced 10 feet apart. They are connected to each other, and to a ground bus inside of the shack ( I used a 3 foot long, 3/4 inch copper pipe), with a 1 inch braided grounding strap. All of the radio equipment, my computer equipment, power supplies, and all other electronics in the shack, are grounded to this bus. The radio tower  is also grounded to another ground rod array. The shield of the antenna cable is grounded at both ends. All of this grounding gives any pulses or stray energy a place to travel that doesn't include my sensitive electronics.
The antenna feed line is protected with an arc plug. An arc plug is two electrodes hermetically sealed in a gas filled ceramic cylinder. Acting like a voltage dependent switch, the Arc-Plug can repeatedly carry large currents to ground for brief periods.

The idea here is to shunt dangerous pulses away from my equipment and harmlessly into the ground.I think this will do it.
The entire project of hardening this equipment cost me a weekend and about $250. As with most of my prepping projects, this one covered likely as well as unlikely threats, and was done for a reasonable cost. My electronics are now safe from the likely event of a lightning strike, and the unlikely event of a man made EMP attack.

1 comment:

Anonymous said...

How Much EMP Shielding is Enough
and How Can my Shielding be Proven?

DoD MIL-STD-188-125 states that an EMP value to use for EMP test compliance is 50,000 V/m from a pulse with a 5 nsec risetime and 150 nsec duration.

Most electronic devices are required to meet
MIL-STD 461, or their commercial equivalent, tailored radiated susceptibility test limits, RS105, of 10 V/m. Thus, the required shielding effectiveness to protect against an EMP burst is 50,000/10 = 5,000 = 74 dB. Add a factor of 2 = 6 dB for safety and the shielding requirement is 80 dB, falling off to small level at 1.0 GHz.

When you buy a shielded product, device, shed home, building, or other, is the source guarantying 80 dB? Who did the EMP testing and did they issue an EMP test compliance certificate?

If you don't know, get the 3d edition of EMP – Protect Family, Homes and Community by Don White and Jerry Emanuelson, and find out who and how EMP shield testing is done. Otherwise, you are probably buying a product that has very highly questionable EMP protection. The EMP Protection book is obtained at or at Amazon.

Walter Christensen