GB617681A - Improvements in or relating to radio navigational aiding systems - Google Patents

Abstract

617,681. Radio navigation. MADDOX, H. F. Nov. 30, 1945, No. 32390. [Class 40 (vii)] In a radio beacon system for indicating at a mobile receiver its bearing with respect to a transmitting station of known location, the transmitted signals are in the form of regularly repeated pairs of short pulses, at least one pulse of each pair being radiated upon a directional beam which sweeps in azimuth over the zone in which bearings are required and the time spacing between the two pulses of each pair being varied in accordance with the instantaneous bearing angle of the beam. As shown in the Figure, the first 5 Ás duration pulses of the repeated pairs are radiated omnidirectionally from the aerial 19 by the micro-wave transmitter 17 under the control of the 1000 c/s. oscillator 14, pulse shaper 15 and modulator 16 and the 2 Ás duration second pulses of the repeated pairs are radiated from the highly directional rotating aerial 20, the timing of the second pulses being controlled by applying the output from the oscillator 14 to the modulator 16 via a 2 Ás pulse shaper and a delay network 23 which is mechanically coupled to the rotating aerial so that the delay. varies linearly from 10 Ás to 510 Ás for a complete rotation. At the mobile receiver, Fig. 4 (not shown), the received pulses are displayed by intensity modulation or as radial deflections on the circular trace of a long-after-glow cathode-ray tube, the trace being produced by applying phase quadrature voltages from a 2000 c/s. oscillator to quadrature deflection coils. The oscillator is synchronized by the first pulses of the repeated pairs which are selected by applying the positive video pulses directly to the control grid of a coincidence valve and through a delay network to the suppressor grid of the same valve, the delay time of the network being slightly less than 5 Ás so that the coincidence valve will be only opened due to the overlap of the two applied potentials when the received pulses are of 5 Ás duration or more. In a modification, the delay network is replaced by a relaxation oscillator generating a 5 Ás pulse which is then differentiated and the trailing edge used as a control potential for the coincidence value. The circular trace is shifted angularly by rotating the deflector coils around the neck of the cathode-ray tube until the spot due to the first pulse is aligned with an index mark associated with the bearing scale and the timing of the second pulse in terms of the bearing angle is then read off directly from the position of the spot due to the second pulse, Fig. 6 (not shown). The system described may be modified by radiating both pulses of each pulse pair from the directional aerial which may be oscillated over a limited angle instead of rotating continuously, and the first pulse may be distinguished by making it a double pulse. A plurality of beacons may be employed either operating at different R.Fs. or at a common R.F. with different pulse widths and/or pulse recurrence frequencies.