Patent GB-594997-A (GB)
Title: Improvements in object detection apparatus of the pulse reflection type
IPC: G01S13/10
Filed: 1944-02-28
Abstract: 594,997. Radiolocation; thermionic valve circuits. WESTERN ELECTRIC CO., Inc. Feb. 28, 1944, No. 3700. Convention date, June 23, 1942. [Class 40 (v)] [Also in Group XXXV] In a pulse reflection type object detecting apparatus, the reflected pulses from a particular object are selected and followed in range by selector pulses which are automatically adjusted in phase to occur simultaneously with the reflected pulses from the particular object by means which produce from the selected pulses. two portions which are equal when the signal and selector pulses are correctly aligned. The receiving system is also subjected to automatic gain control in dependence upon the selected signal only. In the pulse-reflection object-locating system of Fig. 1 (Cancelled), described in the Specification as open to inspection under Sect. 91, oscillator 10 controls the generation by H.F. oscillator 14 and pulse generator 12, which may be of the form described in Specification 477,875, [Group XXXV], of pulses 18 which are radiated from antenna 16. Oscillator 10 also feeds energy to phase-changer 38, the phase-shift of which may be adjusted by means of shaft 40 and handle 42, the phase-shifted energy passing through a phase adjustment device 44 to a generator 34 which produces a relatively broad flat-topped selector pulse. The selector pulse, which may have a duration of 15 microseconds in a system in which the transmitted pulses are 5 microseconds in duration, is employed to unblock the amplifier 24 which is fed with the received pulses 20 from antenna 22 and receiver 48 and is so biassed that only received pulses occurring during a selector pulse are passed. The selected signals are displayed on the cathoderay oscilloscope 26 and appear as vertical deflections 30 on a trace produced by a sweep circuit 46, a distance scale 35 being provided. The selector pulse may be employed to overcome the bias of the amplifier which is so adjusted that no received signal, except the directly received transmitted pulse 28, is of sufficient amplitude to overcome it, or alternatively the selector pulse may provide the anode voltage for the input stage of the amplifier. Amplifier 24 is also provided with an automatic gaincontrolling circuit 25 which operates in accordance with the amplitude of the selected signal only. For accurate distance measurement an accurately phased short pulse 32 is provided by a timing pulse generator system 36 and is superimposed upon the received signal 30, the range being indicated by a dial 39 and pointer 41 associated with the control shaft 40 which is common to the phase-changer 38 and timing pulse generator 36. System 36 may be of the type in which an harmonic of the fundamental frequency of oscillator 10 is caused to generate a series of sharp accurately placed pulses, while a broader pulse derived from the fundamental is employed to select a particular one of the sharp pulses. The fundamental frequency pulse is controlled by a phase-shifter similar to and coupled to the same shaft as phase-changer 38, while the harmonic is controlled by a similar phase-shifter coupled through a suitable gear train, so that a dial 39 and pointer 41 associated with the control shaft 40 and handle 42 indicate with a high degree of precision the distance of an object producing a signal 30 which is brought into coincidence with the pulse 32. This subject-matter does not appear in the Specification as accepted. To facilitate the operation of the system, a second cathoderay oscilloscope 49 is employed on which all reflected signals are displayed. The selector pulse from generator 34 and the precision timing pulse may be superimposed upon oscilloscope 49 by means of switches 11 and 37 to facilitate the selection of a particular signal, and the reflected signals may be removed by switch 23. The selector pulse may be centred with respect to the precision timing pulse by means of the phase adjustment 44. In a modified arrangement forming the subject-matter of the Specification as accepted, Fig. 1, in which means are provided for automatically following changes in range of a selected signal, a single phase-changer 76 is employed and a pulse generator 74 provides the selector pulse 112, Fig. 2A, which is fed through phase adjustment device 44 to the amplifier 24, and a synchronizing wave 114, Fig. 3A, with a sharp change 116 which is fed to a sensing circuit 72. Switches 23 and 37 enable the signals to be removed from, and the synchronizing wave to be superimposed upon, the selector pulse on oscilloscope 49 to enable the selector pulse and the cross-over 118 of the synchronizing wave to be centred by means of the device 44. The sensing circuit 72 is conveniently a balanced modulator and is fed with the selected signal 118 as well as the synchronizing wave, the output of the circuit consisting of pulses of opposite polarity such as 122, 124, Fig. 2B, corresponding to the portions of the selected signal on either side of the cross-over 116. If the synchronizing wave and selector pulse are correctly aligned with the selected signal, the D.C. output from the sensing circuit is zero as indicated in Fig. 2B, while if the signal and synchronizing pulse are not in proper alignment the output of the sensing circuit will be asymmetrical as indicated at 126, 128 and 130, 132 of Figs. 2c and D, and will contain a D.C. component. The output of the sensing circuit may be employed directly to control a reversible motor to adjust the phase of phase-changer 76 or may control an electrical phase-shifting circuit of the type illustrated in Fig. 5 (not shown) in which a condenser and inductance are serially connected across the source of oscillations and the control voltage is applied to the grid of a valve shunting the inductance while the phase-shifted output is obtained across the condenser. When such electrical control is employed, an integrating circuit 50 follows the sensing circuit 72. This integrating circuit. Fig. 3 (not shown), comprises valves 88, 98 which are normally non- conductive and are serially connected across the H.T. supply 92, 100. The charge on a storage condenser connected between earth and the common point of valves 88, 98 is reduced by positive pulses rendering valve 88 conductive and is increased by negative pulses which render valve 98 conductive through the agency of a phase-reversing valve 90. A suitable circuit for the pulse generator 74 is illustrated in Fig. 4 (not shown). The master oscillator output, after passing through the phase-changer is fed through a series resonant circuit to an impulse generating coil, the resulting pulse being limited by diodes to produce the selector pulse. The pulse from the impulse generating coil is also fed, through a diode which removes positive pulses, to the grid of a valve which with its associated resistance, capacities and inductance forms a shaping circuit producing the syn-. chronizing wave.