Jam today

'At the next left, you have arrived at the wrong destination.' Just how vulnerable are we to the loss of GPS signals, and what can we do to reduce the risk from natural or malicious jamming? Christine Evans-Pughe finds out. In January 2007 Captain Matthew Blizard, Commander of the US Coast Guard Centre of Excellence for Navigation (NAVCEN), reported the loss of GPS signals in the Port of San Diego. Not only had the navigation equipment for general aviation stopped working but local telephone switches and cellular phone operations were disrupted, and the hospital's mobile paging system went down. It took Blizard and his colleagues three days to pinpoint the source a two-hour US Navy training exercise in communications jamming between two ships in the area. When the Navy technicians found problems with the GPS systems on the ship under attack, they stopped the exercise but didn't report the incident beyond their usual channels. No one told the GPS Operations Centre in Colorado (GPSOC) or NAVCEN about the exercise because the jamming was not meant to be in the GPS 1 band.