Washington DC
A RUSSIAN device that can reportedly jam Global Positioning System (GPS)
signals over a 200-kilometre radius could provide terrorists with a cheap and
simple means to befuddle aircraft navigation systems.
GPS and its Russian counterpart, Glonass, rely on a network of satellites to
broadcast radio signals which a receiver uses to deduce its position. Since the
satellites don鈥檛 carry large power sources, the signals they broadcast are weak,
which makes them vulnerable to jamming.
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The Russian device, from a company called Aviaconversia, first came to light
at the Moscow Air Show in September. The company announced that it can offer a
portable, 4-watt GPS/Glonass jammer for less than $4000. It claimed that
this low-power device could prevent aircraft from locking on to a GPS
signal.
Testing the device would be illegal in most Western countries. But as news of
the device spreads, GPS experts are taking Aviaconversia鈥檚 claim seriously. 鈥淚
tend to believe them,鈥� says Lawrence Young, a physicist at the Jet Propulsion
Laboratory in Pasadena, California. By broadcasting 鈥渘oise鈥� on the frequencies
that GPS uses, a 4-watt jammer could prevent aircraft from using the satellites鈥�
signals. Young adds that a skilled engineer could probably build a similar
device with components available from a typical electronics store.
The vulnerability of satellite navigation systems to jamming is a growing
concern, as the US Federal Aviation Administration (FAA) intends to start
decommissioning ground-based navigation beacons in 2010.
Les Dorr, a spokesman for the FAA in Washington DC, says the agency is aware
of the problem, but has no plans to reduce its future reliance on satellite
navigation. 鈥淲e are working with the Department of Defense to address
unintentional and intentional jamming,鈥� he says.
Others are more worried. 鈥淭he very fact that jamming the signal is so trivial
means it can cause a disruption near a major airport, and a possible safety
hazard,鈥� says Jim Sennott, an electrical engineer at Bradley University in
Peoria, Illinois. 鈥淚鈥檓 concerned about it.鈥�
The US military also acknowledges the vulnerability of GPS. 鈥淛amming GPS
might be a useful military technique for those who might oppose US and allied
forces,鈥� says James Armor, director of the Department of Defense鈥檚 GPS Joint
Program Office in El Segundo, California.
The encrypted GPS signals used by the military would be harder to jam than
those used by commercial airliners. Among other things, they are spread over a
wider part of the radio spectrum, making them more difficult to compete with.
But a determined jammer could use a more powerful device than the 4-watt Russian
model.
For both military and civilian GPS users, the most obvious way to make
jamming more difficult would be to increase the power of the signals. But this
would require significant changes to the satellites鈥� design.