Patent GB-592574-A (GB)
Title: Improvements relating to the determination of the time interval between an electrical pulse and its echo
IPC: G01S13/18
Filed: 1944-01-31
Abstract: 592,574. Radiolocation ; cathode-ray oscillographs. STANDARD TELEPHONES & CABLES, Ltd. Jan. 31, 1944,'No. 1815. Convention date, Oct. 31, 1942. [Class 40 (v)] [Also in Group XXXVI] A pulse radiolocation system comprises a main and a vernier cathode-ray oscillograph, the time base sweep of the vernier oscillograph, which is provided with calibration marks, corresponding in time with a movable marker pulse on the time base sweep of the main oscillograph. In the radiolocation system of Fig. 1, transmitter 10 radiates pulses 24 from aerial 12 while echo pulses received by aerial 16 and receiver 14 are displayed as vertical deflections on the time bases A-B and X-Y of the main and vernier oscillographs 20, 21 respectively. The time base A-B is produced by the sweep generator 23 under the control of the transmitted pulse, delay devices 26, 27 producing equal delays being inserted in the signal channel and sweep generator control connection to compensate for fixed delays which occur in the equipment controlling the vernier time base. The marker signal 55 corresponding to the interval X-Y on the main time base is produced by passing the pulse 24 through a delay device 31 which is arranged for the adjustment of delay in steps, and feeding the delayed pulse through a pulse sharpener 32, and an interval timer 34 and limiter 36 which produce the waveforms 35 and 38, Fig. 2, respectively. The rectangular pulse 38 of duration t3, delayed a time t2 with respect to the transmitted pulse by means of device 31, is then fed to the grid 51 of oscillograph 21 to illuminate the vernier time base, and is also fed through an attenuator 54 to the grid 50 of the oscillograph 20 to produce the bright patch 55 which enables the control of delay device 31 to be adjusted so that the marker covers a particular echo signal 25 delayed by t1 from the transmitted pulse. The pulse 38 is also applied to a differentiating circuit 40, the output pulses from which are utilized to control the vernier sweep generator 42 producing the waveform 43, and a generator 45 of calibrator pulses 44, such as that described in Specification 592,580, which are displayed on the time base X-Y. As the delay t0 of the delay lines 26, 27 is chosen to compensate for any delay in the vernier time base control system other than the calibrated delay of device 31, the range of an echo 25 is determined directly by the addition of the reading of device 31 and the number of calibration divisions between the signal and the commencement of trace X-Y on the vernier oscilloscope. In order to prevent the echo pulse 25 occurring at the extremity of the trace X-Y, the delay device 31 is preferably provided with steps giving retardation intervals shorter than the duration t3 of the indicator pulse and trace X-Y, so that the echo can always be brought to some point near the middle of the vernier trace. One form of the interval timer, Fig. 3 (not shown), comprises a gasfilled discharge tube which is caused to conduct by the pulse from the pulse sharpener 32, a condenser-resistance biassing combination in the cathode circuit determining the conducting period of the tube and thus the duration of a positive pulse which is fed from the cathode to the limiter circuit 36. In an alternative form of interval timer, Fig. 4 (not shown), the sharpened pulse is applied to the grid of a valve, the anode circuit of which comprises a heavily damped oscillatory circuit, the first half-cycle of the resultant damped oscillation being effective to produce the desired output pulse from the limiter 36. In a modified radiolocation system shown in Fig. 5, the delay lines 26, 27 are omitted and a calibrator 80 is controlled by the transmitted pulse to produce a series of calibration pulses on the main trace A-B. The marker pulse 55 applied as brilliance modulation to oscillograph 20 and also applied to the vernier oscillograph 21 to remove the blackout is derived in the manner previously described by a delay device 31a consisting of two parts 31b and 85. The steps of the delay device 31b produce retardation equal to one-half of the interval between calibration pulses. The sweep generator 42 for the oscillograph 21 is controlled by the calibration pulses to produce a series of saw-tooth waves, the short delay line 85, producing a delay equal to one step of delay device 31b, being switched in and out of circuit on alternate steps of device 31b by means of ganged switching elements 86, 87 and contacts 88, 88a. The saw-tooth sweep voltages are thus moved by half a period on alternate steps of the delay device and the marker pulse which thus remains in step with a saw-tooth wave, and the visible sweep on the oscillograph 21 are shifted along the range of the system in overlapping steps by adjustment of delay device 31a. In a further modification, Fig. 6 (not shown), the sweep generator 42 of Fig. 5 is controlled by calibration pulses without the intervention of the short delay line 55 and the marker pulse is not applied to brighten the vernier oscillograph during the selected period. The marker pulse 55 in addition to providing brilliance modulation on the main oscillograph is employed to open a gate valve in the signal channel to the vernier oscillograph to permit only the signals occurring during the interval of the marker pulse to be displayed on the vernier oscillograph.