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 63 mhz and having specified separation.