A method of high-speed search for DME and TACAN

Heretofore DME and TACAN equipments have depended on slow-moving analog-type search gates to look for a reply to an interrogation. The slow-moving gate was necessary to distinguish the desired reply from among many other squitter pulses or replies meant for other aircraft. This resulted in a variety of long search times varying from 15 to 30 seconds, depending on maximum range, interrogation rate and other factors. This paper describes a new digital ranging technique in which the search gate moves outward from zero miles in discrete large steps, looking for the reply only in those places where it is possible for it to be, rather than wasting time in a continuous search which includes many places where the reply can't be. This results in search times of a fraction of a second and in effect gives the pilot the ability to obtain his range instantaneously.