Criminal gangs have begun to use GPS "jammers" from China to help them steal expensive cars and cargo, and fear that terrorists can use a more powerful version to destroy air traffic, a meeting in London on Tuesday will hear The

The GPS jammer transmits a radio signal at the same frequency on a global positioning system (GPS) satellite, overwhelming the timing signal used by the vehicle to draw its position. This means that a vehicle with a valuable load, or a car with an anti-theft GPS device, if stolen, should report its location and can not distinguish the correct GPS signal.

Some German drivers are also considered to use such jammers to try to escape the GPS-based road charges, which was introduced in 2005. There are also robberies in Russia, which have been used on trucks for GPS systems and mobile phones to prevent drivers from communicating with the authorities.

In Germany, such as in the UK, the sale or use of such jammers is illegal, although imports or possession of these disturbances seem to be legal.

Satnav equipment relies on at least four satellites of 30 satellites that can "see" orbit 20,200 km (12,550 miles) above the Earth: the terrestrial equipment can be calculated by correlating the very precise timing and identification signals they transmit Own position in about 1 meter. However, the interfering device does not have to release a strong signal to disrupt GPS reception.

"The problem is that the signal of the satellite is very weak - this is equivalent to picking up the light output of the 25-watt bulb on the satellite," said Bob Cockshott, another spokesperson. The Technical Strategy Committee, which consists of business, innovation and skills Ministry of Finance.

"This means that you only need an output of about 2 watts of interference signal, you can from the GPS satellite on any signal to a few meters of the place. Such a device than the ground on the GPS signal powerful times.

Cockshott said such a more powerful disruptor could be used for a variety of criminal gangs. "They will work dozens of kilometers, so drug gangs may use them to disrupt the sailing of the Thames, if they are delivering, and do not want their opponents to track them."