Distance measuring equipment
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A DME (Distance Measuring Equipment) is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals.
- A radio pulse takes around 12.36 microseconds to travel 1 nautical mile (1,852 m) to and from; this is also referred to as a radar-mile.
- The aircraft interrogates the ground transponder with a series of pulse-pairs (interrogations) and, after a precise time delay (typically 50 microseconds), the ground station replies with an identical sequence of reply pulse-pairs.
- The DME portion of the TACAN system is available for civil use.