Patent GB-1346465-A (GB)
Title: Range tracking device
IPC: G01S13/70
Filed: 1971-05-28
Abstract: 1346465 Pulse-echo ranging HUGHES AIRCRAFT CO 28 May 1971 [1 June 1970] 18026/71 Heading H4D A pulsed ranging system wherein there is stored a digital signal representing the complement of the digital representation of the time between transmission and reception of an echo during a preselected ranging period includes means for entering in said store the latest complement signal during ranging periods in which an echo is received and means for re-entering the last measured complement when no echo is received. In a laser range-finder a sync. generator causes the laser to transmit a light pulse which itself is detected and fed to a video amplifier along with any echo signals. The video amplifier signals are passed after threshold detection to a digital ranging unit, Fig. 2. A "start" switch 58 is activated sending a negative pulse to clear counter 56, setting bi-stable 62 in the acquisition mode by enabling gate 80 via the bi-stable zero output. The next transmitter video pulse on line 41 coincides with the transmitter sync. signal (A trigger) and sets bi-stable 52 enabling the counters 66, 68. When counter 66 indicates the minimum limit of the acquisition range gate, bi-stable 74 is set causing the outputs of gates 80 and 48 to fall and rise respectively. If no echo is received before counter 66 indicates the maximum limit of the acquisition range gate, bi-stable 78 is set, thereby resetting the outputs of gates 80 and 48 to high and low respectively. When counter 66 is full, gate 122 resets bi-stable 52 stopping the count. If an echo does occur during the acquisition range gate, bi-stable 52 is reset via gate 48 stopping both counters. The echo signal also resets bistable 62 via gate 110 such that gate 80 output rises. Further the contents of register 112 are read into counter 56 which then indicates 001. Monostable 67 is also triggered via gate 46 thereby reading the complement of the contents of counter 66 into counter 68, also bi-stable 82 is reset via gates 94 and 102. At the next transmitter pulse counter 66 is reset to zero and both counters 66, 68 are started again. When counter 68 reaches a full count minus one half of the tacking range gate, bi-stable 82 is set via gate 84 thereby raising the output of gate 48 and enabling gate 110. If no echo pulse is received before the counter 68 content reaches full plus one half the tracking gate width, bi-stable 82 is reset via gates 86 and 102 thus blocking gates 48, 46 and the echo input to bi-stable 52. Thus the count continues until counter 66 is full whereupon gate 122 resets bi-stable 52 stopping the count. The counters are of identical capacity and thus having completed one complete counting cycle, counter 68 reads once more the last measured range. Since no echo was received counter 56 has not been reset to 001 and at the next transmitter pulse its content is increased by one. If four transmitter pulses pass without reception of a valid echo, counter 56 resets bistable 62 reverting back to the acquisition mode by enabling gate 80. If an echo is received during the narrow tracking gate, counters 66, 68 are stopped and monostable 67 is triggered as before. The tracking gate may also be terminated by bi-stable 78 indicating the maximum range of interest. The range measurement is fed to a digital computer and an analogue utilization device only during valid range measurement periods. Radar signals may be used instead of the laser system.