Homemade GPS jammers raise concerns

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 that can jam Global Positioning System (GPS) signals.

Information in the article that appears in the current issue of the online hacker magazine Phrack potentially puts at risk GPS devices used for commercial navigation and military operations, 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 this week called it technically competent and said amateurs with a certain amount of technical skill could build a GPS jammer from the plans.

Although the article said the jammer is designed to work only against civil-use GPS signals broadcast on the frequency of 1575.42 MHz and not the military frequency of 1227.6 MHz, James Hasik, an Atlanta-based consultant and author of the book The Precision Revolution: GPS and the Future of Aerial Warfare, disagreed.

Hasik said that while the Phrack jammer is targeted at civil GPS signals, 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.

Hasik said that GPS receivers are especially vulnerable to jamming because of low signal strength after traveling through space from GPS satellites orbiting 12,000 miles above the earth.

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

Air Force Lt. Col. Ken. McClellan, a Pentagon spokesman, said the implications of homemade jammers described in the article are "somewhat serious" because the use of such jammers "could disrupt commercial operations."

McClellan said GPS experts at the Pentagon do not "at the moment" view homemade jammers as a hazard to flight safety for commercial 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 civilian GPS signals and users by, among other things, "the transfer of appropriate antijam technology from the military to civil use." Mosley was unable say whether that technology transfer has occurred.

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Richard Langley, a GPS expert and professor of geodesy at the University of New Brunswick in Fredericton, New Brunswick, called the implications of home-brew GPS jammers "scary." But he expressed doubt that the Phrack jammer would be very effective against aircraft when used from the ground. However, Langley noted that if a terrorist used the jammer from on board an aircraft, it would extend the range and "hence the effectiveness of the jammer."
James Miller, program manager for GPS at United Air Lines Inc., said the loss of a GPS signal in a commercial aircraft wouldn't "cause a catastrophic event," because airliners operate with multiple navigation systems. But loss of a GPS signal by general aviation aircraft flying solely on GPS could be "quite challenging," he said.
Warren Morningstar, a spokesman for the Aircraft Owners and Pilots Association in Frederick, Md., said general aviation pilots don't use GPS as their sole navigation source and called the potential of jamming a "nuisance" rather than a safety hazard.
"You need to take it seriously anytime there is publicity about things that could disrupt the critical infrastructure," said Mike Swiek, executive director of the U.S. GPS Industry Council in Washington. But, Swiek said, "there is no need for panic. All the GPS systems are monitored for any type of interference." Swiek noted that while "any garden-variety radio engineer" has the knowledge to build a GPS jammer, there have been few reports of any attacks against GPS systems.
Gabe Neville, a spokesman for Rep. Joseph Pitts, (R-Penn.), co-chairman of the House Electronic Warfare Working Group, said news of the Phrack story about jamming indicates that GPS jamming technology is "easily available" and that the Pentagon needs to beef up its electronic warfare research and development budget. But Neville said he doubts a homemade jammer could cause as much damage or disruption as systems acquired and operated by foreign governments.

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Copyright © 2003 IDG Communications, Inc.

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