Patent GB-705361-A (GB)
Title: Improvements in or relating to radar devices
IPC: G01S13/70
Filed: 1945-05-04
Abstract: 705,361. Radio location ; valve gating circuits. WESTERN ELECTRIC CO., Inc. May 4, 1945 [May 12, 1944], No. 11450/45. Classes 40 (6) and 40 (7). [Also in Groups XXXV and XXXVIII] In a radar system, a gating pulse 209, Fig. 5, is produced corresponding to each emitted pulse and its timing is compared with that of a pair of pulses 203, 205, which are produced by delaying the echo pulse 201, so that when the gating pulse occurs out of symmetry with the delayed pulses tracking means are brought into operation to alter the timing of the gating pulse until it is brought into symmetry with the delayed pulses. A third delayed pulse, 204, occurs midway between the pulses 203, 205 and the coincidence of this pulse with the gating pulse actuates an " on-target " indication (e.g. the lighting of a lamp), and controls the operation of a mechanism which in the absence of an echo pulse causes the gating pulse to scan between predetermined time limits and which in the presence of an echo causes the gating pulse to follow the echo pulse so as to remain in coincidence with the delayed pulse 204. Fig. 1 shows a radar system embodying the invention and Fig. 5 shows waveforms occurring at various points in Fig. 1. The echo pulses 201 are passed to the receiver and video amplifier 13 and thence to a delay line 17, from which the three equally spaced output pulses 203, 204, 205 are passed to the gated integrating circuits 24 which comprise three valves the cathodes of which are normally maintained positive with respect to their anodes, each pulse being applied to the grid of one valve. Pulses from the transmitter are passed through a delay line 22 to the range unit 18, wherein the start stop circuit 19 produces a lengthened pulse 206 of length corresponding to the maximum range limit. This passes to a variable R-C delay circuit 20 so that the output of the unit 18 is as shown at 208. The gate forming circuit 23 produces a pulse 209 equal in width to the separation between pulses 203 and 205 which unblocks the cathode bias of the valves of circuit 24 which consequently pass anode current according to the signals on their respective grids. At 220, 221, 222 are shown the current waveforms in the valves corresponding to the pulses 203, 204, 205 respectively, when the gating pulse is centred accurately on the delayed echo pulses, the current due to the pulse 204 being least owing to the signals applied to the grid being negative. Thus under these conditions the voltage output due to pulse 204 is greater than the mean of the other two outputs, which are equal, and so by means of the pulse 204 the presence of an echo signal may be determined while the pulses 203, 205 indicate the alignment of pulse 204 with the gating pulse. The signals produced from pulses 203, 205 are fed to a differential D.C. amplifier 25 the output of which modulates a 400 c/s sinewave in the modulator 26. The output from the modulator controls the operation of a two phase motor 30 which drives the mechanical connection to the delay circuit 20 thereby altering the condenser value and shifting the gating pulse until it is accurately centred between the delayed echo pulses. One or more dials on the range unit give a direct indication of the range. The output from the circuit 25 due to the pulse 204 is taken to the on-range signal circuit 31 together with a signal representative of the mean outputs from the pulses 203, 205. Circuit 31 comprises two stages of direct coupled push-pull amplifiers in the output of which is a relay which determines the operation of the scanning circuit 32. When equal signals are applied to the circuit, i.e. when no echo pulse is present the relay is just not actuated. However when the signals from the pulse 204 increase due to the coincidence of the gating pulse with an echo, the relay operates to a T- position (for tracking the echo). When the relay is in the T-position it has no effect on the output from the circuit 25, but causes a lamp to be lit indicating that a target is being tracked. In the other position, the S-position, the circuit provides an ouput causing the motor to drive the delay circuits 20 between certain limits thereby scanning in range. When the maximum or minimum range is reached a contact is closed which causes a flip-flop circuit to change over and thus reverse the direction of the motor. In the T-position the flip-flop is disconnected so that the motor is operated by circuit 25 only, so that the echo may accordingly be tracked beyond the above mentioned range limits. When the echo is being tracked the circuit may be made to revert to its scanning operation by earthing the output from circuit 25, thus causing the motor to alter speed and removing the gating pulse from the echo and restoring the conditions necessary for scanning. An automatic gain control circuit is provided The mean output from circuit 24 is fed to rectifier 33 the output of which is fed to amplifier 34 which is gated by the pulse 206 from the start-stop circuit 19. Thus the A.G.C. voltage applied to circuit 15 consists of a pulse 207 whose amplitude decreases as the amplitude of the echo pulse increases. Consequently the receiver circuits operate only during the extent of pulse 206 and 207, that is only when echoes are in range. Specification 588,187 is referred to.