Note on a short-range radio position-finding system using modulated continuous waves

The paper describes a position-finding system by which the polar co-ordinates of any suitably equipped aircraft can be determined at a single base station using phase-comparison range-finding apparatus and a v.h.f. automatic direction-finder in conjunction with conventional communication equipment.¿ An experimental model is described in which azimuth and range are displayed on a single cathode-ray oscillograph, which may be installed in an airport control tower. Range is indicated without ambiguity up to 100 nautical miles, and there is no azimuthal ambiguity. So far, the model has been used primarily to demonstrate the principles of the system, in conjunction with an aircraft fitted with an experimentally modified Service type of v.h.f. communication equipment. The results of a limited number of tests suggest that, with airborne equipment specifically designed for use with the system, the probable error in range measurement should be less than 1 mile. Azimuthal accuracy is not here discussed, but in a companion paper it is shown that the probable instrumental error of the direction-finder is less than 1.5 deg, implying a probable lateral error less than 2.5 miles at the maximum non-ambiguous range of 100 nautical miles.