Recent improvements in today´s DME

Today´s DME is defined and its major characteristics listed. Its relationship to TACAN and its current state of implementation are reviewed; 10,000 airborne DME sets have been produced in the last three years. Photographs and major characteristics are given of current airline equipment made by two major manufacturers, general aviation equipment made by a third manufacturer, and of a typical ground transponder. The bulk of the text is devoted to outlines of several new features which can be applied, independently of each other, within present system specifications. For airborne equipment, these include: accuracy of ±180 feet, search time of 0.2 second, self-check, elimination of moving parts, variable transmitter power and pictorial display. For ground equipment, the improvements reviewed include: increased accuracy during variation of interrogation level, elimination of steady-state error, advantages of high-gain antennas and the tailoring of transponder parameters to the expected traffic, an example being given of a transponder weighing less than eight pounds yet capable of serving light traffic at long ranges. It is concluded that, while increased performance is immediately available within present specifications, greater world-wide implementation could occur if certain system specifications were relaxed.