Patent GB-686732-A (GB)
Title: Improved navigation system using radio beacons
IPC: G01S3/68
Filed: 1951-04-25
Abstract: 686,732. Radio navigation. COMMONWEALTH SCIENTIFIC & INDUSTRIAL RESEARCH ORGANIZATION. April 25, 1951 [June 20, 1950], No. 9690/51. Class 40 (vii). A radio-navigation system for guiding a craft comprises a plurality of fixed beacons radiating respective differently characterized signals and on the craft, a receiver having a directive aerial scanning in azimuth, means for rendering the receiver sequentially responsive to the differently characterized signals, and a cathode-ray tube to the intensity-modulating electrode of which the receiver output is applied, the cathode-ray beam being deflected in one direction in synchronism with the aerial scanning and in the perpendicular direction in synchronism with the response sequence of the receiver. In the preferred embodiment, the beacons radiate unmodulated continuous-wave signals of respective-different radio frequencies, and the receiver, Fig. 5, comprises a panoramic receiver, the beam in the cathode-ray tube 31 being deflected in synchronism with frequency sweep of the receiver local oscillator. The display produced in an aircraft 10 flying as shown in Fig. 2a with respect to two beacons A, B will consequently be as indicated in Fig. 2b, the vertical displacement levels A<SP>1</SP>, B<SP>1</SP> corresponding respectively to the beacons A, B. A display as shown in Fig. 3b will similarly be produced when the relative configuration of aircraft and beacons is as shown in Fig. 3a. The receiving aerial 15 comprising a continuously rotating slotted feed and reflector, feeds a balanced mixer 24, the output from which is applied via circuits 28, 29, 30 to the control grid of cathode-ray tube 31. The local oscillator comprises a klystron 32 frequency-modulated by the output from an audio-frequency oscillator 35. A further output from the oscillator 35 is applied to the vertical-deflecting plates of the cathode-ray tube 31. The aerial 15 is rotated by a motor 18 which also drives the wiper arms of the continuously wound potentiometer, the output from which is applied to the horizontal-deflecting plates of the cathode-ray tube. In order to restrict the display to signals received from in front of the aircraft, a switch comprising elements 22 and 43 is closed, thus disabling circuit 30 during the rearward 180 degrees of the aerial scan. A further switch comprising rotary contact 21 and fixed contacts 43, 44 and 45 is provided to produce vertical bright lines on the display corresponding to the straightahead, 90 degrees port and 90 degrees starboard position. Instead of continuously rotating the aerial system may scan to-and-fro over an arc. Alternatively two aerials arranged back-to-back and rendered alternately operative may be used. Automatic gain-control may be provided to prevent signals received by side lobes of the aerial system from affecting the display. The receiving aerial preferably has little vertical directivity so that the passage of the aircraft over a beacon is indicated by the spread of the corresponding indication into a horizontal straight line. In alternative systems the beacon identification may alternatively be effected by the frequency of a modulating signal or by a code modulation.