DME is defined as a combination of ground and airborne equipment which gives a continuous distance-from-station readout by measuring the time-lapse of a signal transmitted by the aircraft to the station and responding back.
- Usually coupled with a VOR beacon, to enable aircraft to measure their position.
- Operates on 960 and 1215 MHz, line-of-visibility b/w the aircraft and ground station is required.
- Provide groundspeed and time-to-station readouts with differentiation.
- DME was a post-war development based on the identification of friend or foe (IFF) systems and similar principles to secondary radar ranging function.
Distance measuring equipment (DME) is a radio navigation technology that measures the slant range (distance) between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band between 960 and 1215 megahertz (MHz).
Line-of-visibility between the aircraft and ground station is required. An interrogator (airborne) initiates an exchange by transmitting a pulse pair, on an assigned ‘channel’, to the transponder ground station.
The channel assignment specifies the carrier frequency and the spacing between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency by 63MHz and having specified separation.