Patent GB-623626-A (GB)
Title: Improvements in and relating to apparatus for use in determining the direction of an object from which radio-waves are being received
IPC: G01S13/68
Filed: 1943-01-29
Abstract: 623,626. Automatic control systems. SPERRY GYROSCOPE CO., Inc. Jan. 29, 1943, No. 1589. Convention date, Jan. 29, 1942. [Class 38 (iv)] [Also in Group XL (c)] In a direction-finding or radiolocation system in which direction is determined by comparing the strengths of signals received by antennµ having overlapping directional characteristics, and in which the received signals are modulated it the same frequency but with different phase, and are then combined, the phase of the resultant signal indicating the direction of the received signal or which antenna is directed nearer to this direction, the antennµ systems are electromagnetic horns and the modulation is effected by rotating a vane in the throat of each horn or in an associated wave-guide. The resultant signal may control a servomotor to make the antenna system follow the target, or to control the director of a gun. Fig. 3 shows a system for detecting and tracking a target in azimuth only, a similar arrangement being used for elevation. Waves transmitted by the horn 2 and reflected by the target are received by horns 4, 5 arranged at a small angle to each other so as to have overlapping characteristics. Metallic vanes 25, 26 displaced by 90 degrees are rotated in the throats of the horns by a motor 28, thus modulating the received signals in different phase. The two signals are combined in the wave-guide 30 and demodulated by a crystal detector 35, the resulting current having its phase determined by the direction of the received wave. This current is led through amplifier 41 in push-pull to the grids of valve 44, the grids also being fed in parallel through transformer 45 by a reference-phase generator 46 driven by the motor 28. The phase of the signal current determines the direction of current through the field coils 50<SP>1</SP> of a dynamoelectric amplifier 50, and consequently the polarity of the D.C. output of the armature which is fed to the motor 12<SP>1</SP> driving the table 3 carrying the horns 4, 5. When the horns receive equal signals, they combine in the wave-guide to form an unmodulated carrier, so that no current of modulation frequency is produced and the table 3 comes to rest. When this balance is upset, the horns automatically track the target. In order to scan the sky, the output or the valve 44 may be unbalanced by removing a short-circuit around resistance 68, whereupon the motor 12<SP>1</SP> continuously drives the horns; as soon as signals are received by either of the horns, a relay 66 short-circuits resistance 68 to restore the automatic tracking condition. Manual control of scanning may be effected by moving switch 75 to bring the amplifier 50 &c. under control of a manuallyadjusted potentiometer 76. A " selsyn " transmitter 15 driven by motor 12<SP>1</SP> conveys data to a director 19<SP>1</SP> associated with gun 60. When the apparatus is modified to determine elevation as well as azimuth, the five horns (one for transmitting and two each for the azimuth and elevation receivers) are mounted on a common support journalled in supporting brackets by trunnions, so that they can be moved in azimuth as in Fig. 3 and in elevation by a separate motor, Fig. 2 (not shown). In a modified system, three receiving horns controlling both azimuth and elevation movements may be used, the modulating vanes being then displaced by 60 degrees, Figs. 5, 8, 9, 11 and 12 (not shown).