Patent GB-684229-A (GB)
Title: Improvements relating to radio systems for the navigation of flying bodies
IPC: F41G7/24
Filed: 1944-04-14
Abstract: 684,229. Radio navigation. COSSOR, Ltd., A. C., BEDFORD, L. H., and JOFEH, L. April 6, 1945 [April 14, 1944], No. 6956/44. Class 40 (vii). [Also in Group XXXV] In a system for navigating a flying body along the axis of a conically swept radio beam, the plane of polarization of the beam rotates at the sweep frequency and a radio receiver on the flying body derives magnitude-of-deviation signals from signals due to beam sweep and direction-of-deviation signals from signals due to polarization rotation. Fig. 3 shows apparatus carried by an aircraft to indicate to the pilot, e.g. in a blind approach system, deviations from a line of flight along the axis of a conically swept radio beam, radiated from a pulse transmitter, the plane of polarization of which rotates synchronously with the sweep. The aircraft carries perpendicular to its longitudinal axis a fixed dipole aerial 10 the pickup of which is thus intensity modulated at the sweep frequency (50 c/s) on displacement of the craft from the beam axis. The amplitude and phase of this modulation are dependent on the magnitude and direction of the displacement respectively. A second modulation component at twice the sweep frequency (100 c/s) is produced by the rotating plane of polarization and its phase is dependent on the attitude of the dipole, i.e. its twist about the longitudinal axis of the craft. The signal from the dipole is rectified, amplified at pulse frequency and detected in a receiver 11, the resulting 50 c/s and 100 c/s components being separated and amplified in stages 12 and 13 respectively. After amplification the 100 c/s component synchronizes a 50 c/s oscillator 14 the output of which is applied to a phase splitter 15 producing two components in quadrature so related in phase to the output of amplifier 13 that a " steer " phase comparator 16 to which one of the components and the output of amplifier 12 is applied gives a D.C. output dependent on the displacement component of the craft perpendicular to the line of the dipole and a " twist phase comparator 17 to which the other component and the output of amplifier 12 is applied gives a D.C. output dependent on the displacement component parallel to the dipole. Phase comparators 16 and 17 are of the type described in Specification 579,299, [Group XXXVI], and their outputs are applied to the deflector plates of a cathode-ray tube 62 thereby producing mutually perpendicular deflections of the spot the position of which thus represents the magnitude and direction of displacement of the craft from the beam axis relative to normally horizontal and vertical axes fixed in the craft. To avoid sense ambiguity through synchronization of 50 c/s oscillator 14 from 100 c/s amplifier 13, this oscillator is correctly phased by closing a switch 64 when the aircraft is flying level to connect the output of a receiver 65, which may be the ordinary communications receiver on the craft receiving, through aerial 66, a transmission modulated at 50 c/s, to terminals 28. Alternatively synchronization may be effected by observing the direction of movement of the spot during a trial turn and operating a reversing switch 63 if necessary. In modifications : (a) Fig. 4 (not shown), dipole 10 is maintained, under gyro control, in a steady altitude relative to vertical so that displacement is indicated relative to horizontal and vertical axes independently of the altitude of the craft; (b) Fig. 5 (not shown), indication as at (a) is obtained by continuous synchronization of oscillator 14 from the output of receiver 65 instead of from amplifier 13. Fig. 2 (not shown), is the circuit diagram of receiver 11 and details of other stages are given.