Patent GB-587185-A (GB)
Title: Improvements in reflection type target locating systems
IPC: G01S19/24
Filed: 1944-09-26
Abstract: 587,185. Radiolocation ; automatic volume control. WESTERN ELECTRIC CO., Inc. Sept. 26, 1944, No. 18411. Convention date, Oct. 1, 1943. [Class 40 (v)] [Also in Group XXXVIII] In.a radar system provided with automatic volume control of received signals, the control is rendered inoperative periodically in order to permit the range of small objects, e.g. shell bursts, giving weak echoes to be observed simultaneously with the range of the larger selected target. In the system described, Fig. 1, pulses from transmitter 16 are radiated and received after reflection from a target by a reflector 32 containing an antenna element 34 which is continuously rotated by a motor 22 producing the effect of a beam rotating in a conical path at a small angle to the axis. Reflected signals from a target not on the axis,will be modulated at the frequency of rotation. These signals after detection are applied to the vertical-deflecting plates of a cathode-ray tube 60 and a movable step is provided on the trace by a variable control unit 68 so that when the step is aligned with a selected pulse, the setting of unit 68 will give a measure of the range. A gate circuit 65 is also controlled by the step voltage so that only the selected pulse passes through amplifier 70 to control the directionindicating circuits and the A.V.C. circuit 54. A blanking-pulse generator 62 controlled by pulse generator 12 renders the A.V.C. circuit ineffective for, say, one pulse in four so that shell bursts or splashes near the selected target will be indicated on tube 60. The blanking-pulse generator 62 comprises a double-triode multivibrator, Fig. 2 (not shown), with a condenser - resistance combination which causes the circuit to change over at, say, each fourth pulse, thereby transmitting a negative pulse to the A.V.C. circuit 54. A diode connected to the output circuit prevents the transmission of a positive pulse following the negative. To obtain directional indications, the low-frequency modulation on the reflected pulses is selected by filter 74 and compared in phase with two reference voltages supplied in quadrature by a generator 20 driven by motor 22. The D.C. currents produced by the phase comparison are applied to a second cathode-ray tube 86. A zero signal indicator circuit 94' applies 60-cycle current to the tube 86 when no signals are being received, causing a small circle to be traced around the centre of the tube screen. As signals come in, the circle becomes smaller or reduces to a spot, the latter indicating that the signals are of sufficient amplitude to give reliable indications. The spot also shifts from the centre to indicate the displacement of the target from the axis 'of reflector 32. The zero indicator circuit 94 comprises an indirectly -heated double triode 408, Fig. 5, the heater circuit 418 of which is fed from the 60-cycle source. The grids and heater are coupled so that equal and opposite 60-cycle voltages are applied to the grids giving equal and opposite voltages across anode load resistances 404. The two outputs are connected over terminals 430, 436 to one pair of deflecting plates of tube 86, Fig. 1, and through phase-shifting networks 424, 426 and terminals 432, 434 to the other pair of plates. Bias produced by the detector 72, Fig. 1, controlling the A.V.C. circuit is also applied over terminal 400 to the two grids of valve 408 and the circuit and bias potentials are so proportioned that the indicator ray will trace a circle or spot according to the amplitude of the selected pulses as referred to above. Phase-comparison circuits, Fig. 4. The four modulators 78, 80, 82, 84 of Fig. 1 each include a multigrid valve with two control grids. The valves are grouped in two pairs 316, 318 ; 320, 322 controlling respectively the pairs of deflecting plates of the indicator tube 86. One signal output from the device 76, Fig. 1, is fed via terminal 300 to one of the control grids of valves 316, 320 and the other output, 180 degrees out of phase, via terminal 302 to the corresponding control grids of valves 318, 322. One sinusoidal reference. voltage from generator 20, Fig. 1, is fed via terminal 304 to the other control grids of the valves 316, 318 and the other sinusoidal reference voltage, 90 degrees out of phase, via terminal 306 to the other control grids of valves 320, 322. The output of each valve is proportional to the phase difference between the reference voltages and the signal voltages on its control grids and the cathode ray of the indicator 86 is thereby deflected in accordance with the phase of the signal modulation as compared with the phase of the reference voltage generator 20. Bias for the valves is derived from a potential source 338 through resistance networks denoted generally by 384, 328, 326 and suitable filter systems 372 are provided in the outputs of the valves. Ganged potentiometers 354, 356 and 364, 366 and a potential source 342 provide for centring the cathode ray for the condition of zero signal.