Radar mile

A radar mile is the round-trip pulse travel time for one nautical mile of range, equal to 12.36 microseconds (6.18 microseconds each way at the speed of light, 299,792 km per second, over 1,852 metres). A marine radar derives range by timing the interval between transmission and echo return, then dividing the elapsed microseconds by 12.36 to read distance in nautical miles. The figure sets the timebase calibration of the display and the pulse-repetition-frequency ceiling: maximum unambiguous range must fit inside one inter-pulse period, so a higher PRF shortens the range scale.