distance-measuring equipment

distance-measuring equipment

[′dis·təns ‚mezh·ər·iŋ i′kwip·mənt] (navigation) A radio aid to navigation that provides distance information by measuring total round-trip time of transmission from an airborne interrogator to a ground-based transponder and return. Abbreviated DME.

distance-measuring equipment (DME)

A radio navigation aid operating on frequencies in the ultrahigh frequency (UHF) spectrum between 962 and 1213 MHz and that measures the slant range of the aircraft from the ground transmitting station. In this system, the aircraft transmits a series of pulses in pairs. The ground station receives these pulses and radiates them back at a different wavelength (frequency) after a time interval of 50 microseconds. The airborne equipment measures the time elapsed between the transmitted and the received signals, subtracts 50 microseconds, and displays the result as the distance from the ground station. Operating on the line-of-sight principle, DME furnishes distance information with a very high degree of accuracy. Reliable signals may be received at distances up to 199 NM (nautical miles) at the line-of-sight altitude with an accuracy of better than ¼ mile or 3% of the distance, whichever is greater. See also line-of-sight reception.