Navigation system which provides distance information from ground station to aircraft and broadcasting in the UHF band. İt is generally used as adjoint with VOR/ILS and deployed into the ILS/Glide Path Stations. Therefore, pilot is able to get direction and distance informations simultaneously. Selecting the VOR/ILS frequency enables the DME frequency automatically in such system. 

 

Operation Principle: There are transponder antennas both in the aircraft and ground station. The interrogate signal sent by the aircraft is evaluated in the ground station and to be sent to aircraft as reply signal. Evaluating of the interrogation signal takes 50 usec. The operation principle of the system based on measuring of transmitting-receiving time. Puls modulation is used for communication. After the pilot selects the first interrogation signal, puls pairs began to be sent to ground station. İn this case aircraft is in the searching phase.