Patent GB-590593-A (GB)
Title: Improvements in or relating to radio locating apparatus
IPC: G01S7/08
Filed: 1943-08-27
Abstract: 590,593. Radiolocation; pulse generating circuits; wave guides. COCKCROFT, J. D., BUTEMENT, W. A. S., KEMPSTON, A. E., FARLEY, F. J. M., and VOLLUM, C. H. Aug. 27, 1943, No. 14057. [Class 40 (v)] In a radiolocation system em. ploying pulses of ultra-short waves transmitted in a beam which is continuously oscillated over a small angle in azimuth, a main cathoderay tube shows the disposition and range of all reflecting objects within the field of view and one or more auxiliary cathode-ray tubes show on an enlarged scale any selected part of the image on the main tube. The invention is stated to be particularly applicable to the location of shell bursts producing splashes in the sea in the vicinity of a target under gunfire. The time-base for the horizontal-deflecting plates of the main and auxiliary tubes is synchronized with the oscillation of the transmitting beam, but the timebases for the vertical-deflecting plates are different, corresponding to different ranges, e.g. 40,000 yards and 2000 yards respectively. Transmitter and receiver arrangements, Figs. 1, 1A. A magnetron 1 generating 3 cm. waves is triggered by an alternator 3 to emit pulses at the rate of 2000 per sec. The magnetron is connected to a wave-guide 4 having an extension 5 which is oscillated by a motor 9 through an angle of 6 degrees at a frequency of 4 cycles per sec. The extension 5 carries four dielectric rods 7 fed in phase from the wave-guide and arranged at the focus of a reflector 8 having. a, circular section in the horizontal plane and a three-sided polygonal section in the vertical plane. The joint between the two wave-guide sections 4, 5 comprises plates 61., 62 constituting a capacity coupling, the plate 61 having narrow slots 63 a quarter-wavelength deep and a quarter-wavelength from the edges of the guide. The section 4 of the guide includes tuning means 68 comprising two glass rods moving in a slot and adjustable as regards their protrusion into the guide and their distance from the end of the guide in order to match the magnetron to the guide. The section 4 also includes a gas cell 19 comprising a slotted diaphragm extending across the branch at a distance of half a wavelength from the mouth of the branch, the cell being ionized by the transmitted pulses so as to effectively short-circuit itself whilst acting as an infinite impedance during the reception of reflected pulses. A branch 12 of the wave-guide includes a gas resonator sparkgap 17 of the kind described in Specification 589,023 which acts as a short-circuit for transmitted pulses, but passes reflected pulses to the mixer 13. The mixer consists of a tunable chamber fed with local oscillations through a probe 15 and including a crystal 14 resonant at the intermediate frequency and insulated from the wall of the chamber by a mica spacer which permits I.F. energy to pass to the concentric line 65 whilst short-circuiting any R.F. energy to earth. The Provisional Specification shows a modified arrangement in which the oscillated wave-guide is connected to' the transmitter through a concentric line and includes aT-branch leading to the mixer, this branch including a resonant cell comprising a spark-gap and a distortable diaphragm. General operation of'system. The horizontaldeflecting plates of the main and auxiliary cathode-ray tubes 20, 21 are fed with a timebase derived over terminals 67, 120 from a generator 57 driven by the motor so that the electron beams oscillate horizontally in synchronism with the transmitted beam. The vertical-deflecting plates of the main tube 20 are fed with a slow time-base generated by relaxation relay 22 and valve 23 and locked to the transmitted pulses. These saw-tooth waves are also fed to a double-triode valve 26 which produces in circuit 75 impulses of the same repetition frequency as the transmitted pulses, but spaced from them by a. time-interval dependent on the setting of potentiometer 27. These impulses are converted into sharp positive signal-selecting pulses by pulse generator 30 and applied to the suppressor grid of a gate valve 36. Impulses from relay 22 are also applied to a sine-wave generator 31 feeding the stator coils 32, 33 of a radio-goniometer, the rotor coil 34 of which is coupled to the potentiometer 27. The output of coil 34 is fed to a shaping network 35 giving a. succession of short positive pulses or " calibration pips " separated by time-intervaLs corresponding to 1000 yards. These are applied to the control grids of gate valves 36, 43. When a signalselecting pulse and a calibration pip reach valve 36 simultaneously, an impulse is transmitted to saw-tooth generator 39 to initiate the vertical scanning in the auxiliary tube 21. The next calibration pip is passed by gate valve 43, the signal-selecting pulse still persisting, to create a marker pulse which is applied to the cathodes of the tubes 20, 21. These marker pulses produce horizontal lines of bright dots across the screens of the tubes, the position of the line across tube 20 being variable with the setting of potentiometer 27, whilst that across tube 21 is fixed at the centre. The operator adjusts potentiometer 27 until the marker line on tube 20 intersects the image of a selected target and that image then appears on tube 21 in magnified form as regards the vertical dimension. Further movement of potentiometer 27 brings the image on to the centre marker line and the setting of the control handle gives a measure of the range. Additional marker lines at 200-yard intervals may, be provided on tube 21. Connections from circuits 22, 38 to the control grids of the indicator tubes serve to brighten the images. Two more auxiliary tubes may be connected to circuits 54, 55 showing respectively the bearing of the target and the angular deviation of the shell-splashes. Detailed operation of valve circuits, Figs. 2, 2A. Impulses from modulator 2, Fig. 1, are applied through valve 71 to cross-coupled valves 72, 73 producing reference pulses at the signal-repetition frequency which are applied. to the suppressor grid of the saw-tooth generator 23 having a time-base condenser 24 connected between control grid and anode and a charging resistance 25. Saw-tooth sweep waves providing a time-base corresponding to a range of 40,000 yards are supplied over terminal 69 to the vertical-deflecting plates of the main tube 20. The saw-tooth waves are also applied to the left-hand grid of a double triode 26, the right-hand grid of which is fed by potentiometer 27. The common cathode is connected to a high negative potential over a high resistance, and a diode 29 connects the left-hand grid to the high-potential end of the potentiometer 27. The circuit of the right-hand part of the valve is cut off until the fall of potential on the left-hand grid due to the saw-tooth current causes the potential on the right-hand grid to rise sufficiently for the right-hand branch to conduct. A series of pulses is thus produced in circuit 75 having the same recurrence frequency as the transmitted pulses, but spaced from them by a time interval which varies with the setting of potentiometer 27. These pulses pass to the pulse generator 30 comprising a valve 79 acting as a transitron oscillator and producing sharp positive signal-selecting pulses which are applied to the suppressor grid of gate valve 36. Impulses from valve 71 are also fed over lead 83 to a sine-wave generator 31 comprising a shock-excitation valve 85 with a timed circuit 86 in its anode circuit, a second valve 87 cathode-coupled to a third valve 88 which is back-coupled to valve 85 to offset damping, and a fourth valve 90 connected as a cathode follower. The sine-wave output of valve 90 is fed to the stator coils 32, 33 of a radio-goniometer so that the phase of the sinewave in the output of the rotor coil 34 will depend on the orientation of this coil and this phase is linked to the relative spacing of the transmitted and signal-selecting pulses by a mechanical coupling between rotor coil 34 and potentiometer 27. The output of coil 34 is applied to a shaping circuit 35 comprising an, amplifier 92, a diode 93 and a pair of shaping valves 94, 95 producing sharp positive calibration pips fed over lead 98 to the control grids of gate valves 36, 43. Valve 36 only passes a calibration pipe when a signal-selecting pulse is also present, the latter being long enough for two successive pips to pass. The first pip controls, through a buffer valve 100 and two cross-coupled valves 101, 102, a fast-time-base generator 39 including a charging resistance 104 and a time-base condenser 105. The sawtooth waves generated are then applied through amplifiers 41, 42 to the vertical-deflecting plates of the tube 21. to start the 2000-yard sweep. The output of valve 102 is also applied through a phase-reversing valve 38 to the suppressor grid of the second gate valve 43 so that the second calibration pip passes over terminal 109 to amplifier 50, Fig. 1, and thence to the cathodes of tubes 20, 21 to produce horizontal marker lines. Further marker lines across tube 21 at 200-yard intervals are produced by a sine-wave generator 44 coupled through a phase-adjusting bridge 45, amplifier 115 and shaping valves 116, 117 to amplifier 52. Alternatively, the 200-yard marker lines may be produced by using the fifth harmonic of the output of the coil 34. The oscillating sweepvoltage for the horizontal-deflecting plates of tubes 20, 21 is derived from a sine-wave generator 57 driven by motor 9 and connected through a smoothing circuit 58, Fig. 2A, phaseadjusting bridge 59, balancing resistances 121 and a pair of amplifiers 60.