GPS jammers raise concern

US government officials and communications experts are assessing the public safety and security implications of a newly posted online article that provides directions for making cheap devices to jam Global Positioning System signals.

Information in the article, in the current issue of an online hacker magazine called Phrack, potentially puts at risk GPS devices used for commercial navigation and military operations purposes, authorities said.

The Phrack article provides a detailed guide to building a low-cost, portable GPS jammer out of components that can be easily obtained from electronics supply houses.

According to the article, the "onslaught of cheap GPS-based navigation (or hidden tracking devices) has made it necessary for the average citizen to take up the fine art of electronic warfare." Electronics and GPS experts who read the article last week called it technically competent and said amateurs with a certain amount of technical skill could build a GPS jammer from the plans.

Though the Phrack article said the jammer was designed to work only against GPS civil-use signals broadcast on the frequency of 1575.42 MHz and not the military frequency of 1227.6 MHz, James Hasik, a consultant and author of The Precision Revolution: GPS and the Future of Aerial Warfare, disagreed.

Hasik said that while the Phrack jammer was targeted against the civil GPS signal, known as the C/A code, it could also threaten military systems, since "almost all military GPS receivers must first acquire the C/A signal" before locking onto the military signal, known as the P(Y) code. He added that GPS receivers are especially vulnerable to jamming because of the low level of the signal after it travels 20,000 miles through space from GPS satellites.

The U.S. Department of Defense, which faces the possibility of its GPS-guided weapons encountering Russian-made GPS jammers in Iraq, has antijamming technology at its disposal. Still, the DOD viewed the Phrack article with concern.

Air Force Lt. Col. Ken. McClellan, a Pentagon spokesman, called the implications of the homemade jammers described in the Phrack article "somewhat serious." Such jammers "could disrupt commercial operations," he said. He said GPS experts at the Pentagon don't "at the moment" view homemade jammers as a hazard to safety of flight for civil aircraft or ship operations, "but rather a nuisance."

The Federal Aviation Administration is developing a nationwide GPS-based precision landing system. And the Coast Guard operates a GPS-based maritime navigation system on both coasts, the Great Lakes, inland waterways and Hawaii. Bill Mosley, a spokesman for the Department of Transportation, the parent agency of the FAA and the Coast Guard, said his department is well aware of the threat posed by GPS jammers.

The DOT's John A. Volpe Transportation Systems Center in Cambridge, Mass., prepared a report in August 2001 that said, "Some jamming devices/techniques are available on the Internet and proliferation will continue, because a single device that could disrupt military and civil operations worldwide would be attractive to malicious governments and groups."

As a result of that study, Mosley said, Transportation Secretary Norman Mineta last March ordered an "action plan" to protect civil GPS signals and users by, among other things, "the transfer of appropriate antijam technology from the military to civil use." Mosley was unable to say whether that technology transfer has occurred.

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Bob Brewin

Computerworld
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