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GPS Jamming

Oct
10
2005

Avweb has posted an in depth article discussing GPS Jamming. While the discussion is targeted towards aviation GPS uses, it is an interesting read for anyone interested in GPS technology.

GPS is particularly vulnerable to jamming, because the receivers are exquisitely sensitive — they have to be, to receive the extremely weak signal from orbiting satellites. A relatively low-powered jammer, transmitting static on the GPS frequency band, can overpower legitimate GPS signals over a wide area — as much as a 100 kilometer circle at just 1 watt radiated power.

The article talks about how vulnerable the current GPS system is, what risk it poses to pilots, and how to plan ahead for GPS outages.

The situation for VFR GPS receivers is more problematic, according to Braasch: “Sometimes a VFR GPS will give you a message about low signal strength, poor GPS coverage, or low accuracy, or too few satellites in view. If you drop below four satellites, a lot of VFR GPSs will drop into a 2-D position, where it assumes you’re at constant altitude — you’re at reduced accuracy at that point, and as soon as you start descending or climbing, the position will be false. The catch is that a VFR GPS isn’t required to issue any warning at all — it may just continue to report an inaccurate position, so it’s vital for the pilot to cross-check what the GPS says with other forms of navigation.”

Interestingly, there is a company near me called Crossrate that is currently working on building a device that acs as a GPS receiver as well as an Enhanced Loran (ELORAN) receiver in one device. The two would work in harmony and bad GPS data could be detected by a discrepancy from the ELORAN data and the device could continue to provide accurate location data.

GPS is an exceptional system that is integrated into society.  The challenge to users occurs when GPS information becomes unavailable.  CrossRate Technology is solving the GPS vulnerability problem by integrating eLoran and GPS into a single receiver.  To the user it does not matter if the information comes from GPS or Loran as long as the information is accurate.  Both GPS and Loran have vulnerabilities but the combination of these two systems will provide the user information 99.99999% of the time.  In addition, the combination of the different attributes of these two systems will increase the total space the receivers can be used. 

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