Patent GB-592617-A (GB)
Title: Improvements relating to radio detection systems for measuring the distances of obstacles
IPC: G01S19/35
Filed: 1944-02-11
Abstract: 592,617. Radiolocation. STANDARD TELEPHONES & CABLES, Ltd. Feb. 11, 1944, N6. 2609. Convention date, Oct. 8, 1942. [Class 40 (v)] In a radiolocation system in which echo pulses are displayed on a cathode ray oscillograph, a movable indicator or strobe pulse is produced by generating two trains of pulses of slightly different frequencies in controlled time relation with the transmitted pulse, and combining the trains of pulses so that a pulse of larger amplitude is produced when pulses of the two trains coincide, the larger amplitude pulse being employed as the indicator pulse. The radiolocation system, Fig. 1, comprises a pulse transmitter 10 and aerial 18, and receiver 12 and directive aerial system 19, the receiver being blocked during transmission by the circuit 20. signals from the receiver are displayed as vertical deflections on the main cathode ray oscillograph 14 which may cover the whole or part of the total range of the equipment, and the vernier oscilloscope 116. The generation and timing of the time bases for the oscillographs and the reference pulse 110 is controlled by pulse retarding devices 25, 65, fed with pulses from the transmitter. Simultaneously with the transmission of pulses, energy is fed over connection 22 and decoupling devices 28, 29 to shock excite circuits 26, 27 which are tuned to slightly different frequencies. The transmitter pulse and one train of oscillations are shown in Fig. 2a and b. The oscillations are fed to pulse generators 30, 32, a pulse shifting or delay device 35 being inserted in one channel, to produce series of pulses 40-50 and 40a-50a, which although shown all of equal amplitudes in Fig. 2d and e, actually are of diminishing amplitude due to the decay of the oscillations in the tuned circuits as shown in Fig. 2b and c. The pulses are then passed through decoupling devices 30a, 32a, and mixed to produce large amplitude pulses 40b, 50b. Fig. 2g. Pulse 50b is of smaller amplitude than 40b due to the exponential decay, and a limiter 52 selects the pulse 40b which is fed to the sweep generator 54 to initiate the time base trace A-B on the oscillograph 14. The trace A-B may be arranged by adjustment of the sweep generator 54 to cover any desired proportion of the range of the equipment while adjustment of the phase shifter 35 controls the phase of the beat between the two trains of pulses d and e, Fig. 2, and thus the timing of the commencement of the trace with respect to the transmitted pulse. The beat-pulse 40b is also employed to control the reference pulse 75, the timing of which measures the range of an echo with which it is aligned, and the vernier oscillograph time base X-Y. The pulse 40b is fed over connection 56 to the coil 58 of the vernier delay device 60, the delayed pulse being fed to the further delayed pulse generating circuit 65. Circuit 65 is similar to circuit 25, comprising decoupling devices 66a, 67a, and shock excited circuits 66, 67, tuned to slightly differing frequencies which are followed by pulse generating circuits 70, 72, the outputs of which are passed through decoupling devices 70a, 85 and combined in a limiter 74 to produce a single beat pulse which is applied through decoupling device 86 to produce the indicator pulse 75 on the screen of the oscillograph 14. A switch 87 is provided to enable the indicator pulse to be applied to the deflecting plates or to an intensity or accelerating control electrode 90 to produce a variation in intensity or width of the trace. A delay device 80 is provided after the pulse generator 72 to enable the position of the indicator pulse 75 to be varied. Movement of delay device 80 causes the indicator pulse to move in steps corresponding to the intervals between pulses 40, 41, &c., Fig. 2d, and in order to provide a smooth control of the pulse position, the vernier delay device 60 is employed. The device 60 is provided with a large number of contacts for fine adjustment and is coupled through a reduction gearing 96 and Geneva gearing 98 of a counter 100 to the shaft 101 upon which the control-arm of the delay device 80 is mounted. Continuous rotation of the contact arm 95 of device 60 thus causes continuous movement of the indicator pulse 75, the Geneva gearing causing the contact arm 84 of delay device 80 to advance one step each time the contact arm 95 passes from the end contact 102 to the starting contact 103 of device 60 and vice versa. The wheels 105 and 106 of the counter may be suitably calibrated with 100 and 10 divisions respectively and a third wheel may be added if necessary. The fine divisions of wheel 105 may be arranged to correspond with any desired distance, such as 10 yards, and when the indicator 75 is aligned with an echo such as 110 the reading of the counter plus the reading of the phase shifter 35 will indicate the range of the echo. If desired the phase shifter may be coupled to the counter 100 to give the total range reading directly. For more precise alignment of the reference indicator. and echo signal the vernier oscillograph 116 is provided, the time base X-Y being produced by a sweep generator 112 controlled by the indicator pulse. The sweep generator 112 is adjusted to produce a faster sweep than the generator 54 so that the sweep X-Y comprises only a small part of the sweep A-B containing the echo 110 with which the indicator pulse is approximately aligned. Energy of the echo signals from the receiver 12 is fed to the deflecting circuit of the vernier oscillograph through a delay line 115 which retards the signals by an amount equal to one half of the sweep X-Y so that when the indicator pulse is adjusted to be in exact coincidence with the echo signal 110 the signal will appear at the centre of the oscillograph screen, indicated by the line 120. The delay device 115 may alternatively be connected to delay the indicator pulse so that the sweep for the vernier oscillograph commences half the period X-Y earlier than the indicator pulse, Fig. 5 (not shown). . In a modification, Fig. 3 (not shown), the oscillatory circuits of the delay system 65, Fig. 1, are replaced by a system employing pulse generation by the use of delay lines. The transmitter pulse, after passing through the vernier delay devices 60, is fed through decoupling circuits in parallel to delay lines 131, 141 and amplifiers 134, 144, the outputs of the amplifiers being fed back to the inputs of the delay lines to produce at those points, series of pulses such as those shown at d and e, Fig. 2. The spacing of the pulses is determined by the delay characteristics of the lines and may be such as to provide a predetermined number of pulses during the sweep interval of the oscillograph. The delay devices 60 and 80a (corresponding to 80 of Fig. 1) are shown coupled so as to produce a continuous drive through gearing, the arm 184 of device 80a being arranged to cross the gap between adjacent contacts 115 when arm 95 of delay device 60 passes between the end and starting-contacts.