EMI – Radar and Microwave

Last Updated on 02/18/2015 by dboth

Similar to radio and TV, radar and microwave sources, also a form of RFI, can also affect your computer and crash Linux or any other operating system, especially when they are close by. An airport or air station can be the source of ground-based radars as well as aircraft radars and other radar and radio signals. These signals can be strong enough to cause problems similar to those caused by radio and TV signals.

Microwave relay towers and cellular — mobile — phone signals and their relay towers can cause EMI problems with computers, too. Some police band radar detectors can detect radar signals near cell phone towers and airports. Try driving by a fast food restaurant with a microwave oven operating or going past a bank with an activated security system or a grocery store with radar-operated automatic doors. Each of these is a source of radio and radar waves detectable with your radar detector. Computers pick up these signals too, and it can cause them to crash or at least to act funny.

The Airbase

For several years in the late 1980’s and early 1990’s, while I was working at the National PC Support Center for IBM, our offices were dead straight off the end of the Dobbins Air Force Base runway in Marietta Georgia. Many different types of aircraft flew directly overhead every day, from the C-5’s that were undergoing wing replacement at the factory there, to stealth fighters on their way to the Middle East during the first Gulf War.

There were days that we could get very little accomplished as our equipment crashed fairly regularly. The ones that got the worst of it were the ISA bus computers. The IBM MicroChannel computers fared significantly better because the MicroChannel bus was designed for better resistance to EMI problems. With a strong enough signal, such as from aircraft flying very low overhead, almost any computer will crash.

Microwave oven

Just today (September 09, 2014) I was using my Kindle HDX to browse through my FaceBook account when I got the message on screen that I could post messages while offline. I checked the signal strength icon and it was gone. My wife had just started the microwave to heat the broccoli. As soon as the microwave stopped, my wireless signal returned.

In this case the microwave oven leaks enough radiation to jam the wireless signal even though I was about 15 feet from the microwave when this occurred. You should find that scary.

The Fix

There is no inexpensive fix for this type of problem. The two options you have are both expensive for a business.

The first is to enclose the building or at least the computer room in a Faraday cage which will prevent the ingress of radar and microwave signals into the protected volume. This is extremely expensive to do and is best done during the construction of the building. Of course the secondary benefit is that the Faraday cage also prevents signals leaking out of your computer from exiting the protected volume. The CIA and NSA as well as other organizations that need high levels of security use Faraday cages to keep external spies from detecting the signal emissions from their computers.

The second option is to move your business, computer or Kindle away from the source of the signals. And stay far away from the microwave oven.

Entry Paths

First, radiated EMI can gain access through openings in the computer case. These access points can be caused by running the computer without the side of the case in order to facilitate easy access for various reasons and cover plates left off of the bus slots in the back of the computer. EMI can also infiltrate a computer even through a cover that is merely set in place and not fastened down with the appropriate screws.

Cables connected at one end to the computer but left dangling at the other end while a peripheral is disconnected can act as antennae to capture signals and draw them into the computer.

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