Patent GB-590504-A (GB)
Title: Apparatus utilising a rotating radio beam for affording a visual plan indication of the postion of remote objects
IPC: G01S7/22
Filed: 1944-07-07
Abstract: 590,504. Radiolocation. WESTERN ELECTRIC CO., Inc. July 7, 1944, No. 13066. Convention date, Dec. 20, 1941. [Class 40 (v)] In an object-locating apparatus a highlydirectional energy beam sweeps the area about the observation point and reflected energy is used to provide a visual plan. indication of the area, in which all reflecting objects are displayed at their proper azimuth angles and proportionate distances from a central reference point representing the observation-point. In the radar system of Fig. 1, an aerial comprising a dipole 20 and reflector 22 which is sharply directive in the horizontal plane, but less directive in the vertical plane to allow for roll when mounted on a ship, is rotated about a vertical axis by motor 46, connections being made through slip rings 26, 27 to a pulse transmitter 34 and receiver and amplifier 36. A duplexing unit 32 permits the single aerial to be employed and may comprise sections of transmission line arranged so that the transmitter and receiver each present a high impedance to energy of the other circuit and may also include a voltage-operated device for blocking the receiver input during transmission. The receiver 36 is arranged. with short time constant coupling circuits so that it recovers rapidly from overloading and its output is applied to the grid 58 of the cathode-ray oscillograph 52 to produce intensity modulation of the electron beam. The time-base voltages which cause the electron beam to scan the C.R. tube screen radially as shown at 172, Fig. 5b, and to turn about the centre of the screen in synchronism with the aerial rotation, are produced by the outputs from a sine wave generator 42 on the aerial shaft 38 and a saw-tooth generator 48 triggered by transmitter 34, which are combined in circuit 50 amplified at 51 and fed to the horizontal and vertical deflecting plates 54 and 56 of the C.R. tube. The combining circuit 50, Fig. 2 (not shown), comprises two balanced modulators fed directly witH the saw-tooth wave on one input and fed on the other input with 90 degrees displaced sine waves obtained by means of a phase-shifting network from the generator 42 or by means of a two-phase generator. The outputs from the modulators consist of two 90 degrees displaced sine waves modulated by the higher frequency saw-tooth wave. In order that fixed points on the C.R. tube screen may correspond to compass directions when the equipment is mounted on a craft, the phase of the sine waves fed to the modulators may be controlled. by phase-shifters mechanically connected to a compass. In order to provide bearing indicator lines 174, Fig. 5b, and range-indicating circles 220-226, Fig. 8b, intensity modulation is applied to the cathode-ray tube via the amplifier feeding signals to the tube grid. A commutator 114, Fig. 6, has conducting segments 116 which co-operate with a contact 120 to short-circuit a portion of the bias resistance 128 of one stage 130 of the signal amplifiers and cause intensity modulation of the C.R. tube trace for predetermined azimuth directions ,as the commutator rotates in synchronism with the aerial. To produce the range circles at fractional intervals of the maximum range which corresponds to the pulse recurrence period, energy of the transmitted pulse is fed to an harmonic producer 184, a harmonic of the pulse frequency (4th for four range intervals) being selected by a filter 186. The selected harmonic is amplified at 188 and fed to a pulseproducing circuit 190, which may be of the type described in Specification 477,875, [Group XXXV], producing positive and negative pulses which are applied to the normally cutoff valve 196. The negative pulses in. the output of valve 196 are introduced into the grid circuit of valve 144 of the signal amplifier and produce intensity modulation of each timebase trace at quarterly intervals, the marks tracing out the range circles as the aerial rotates. Switches 119, 195 are provided to select the calibration marks required.. The invention is stated to be applicable to systems utilizing compressional waves and also to systems employing the frequency modulation method for distance determination. Specification.s 520,778, 542,634 and 546,202, [Group XXXIX], also are referred to.