| 摘要 |
1,204,296. Laser radar. BOFORS A.B. 17 April, 1969 [17 April, 1968], No. 19747/69. Heading H4D. [Also in Division G1] In a light pulse, e.g. laser, ranging receiver, wherein noise rejection is provided by imposing a fixed threshold below which pulses are not passed from the detector to the utilizing means, the maximum operating range of the receiver is limited to that at which the target echoes are greater than said threshold. To overcome this drawback the invention proposes varying the relation between the threshold and amplitude of the pulses produced by the detector in dependence on the number of pulses occurring above the present threshold, whereby for example in the case of a " quiet " background the threshold may be lowered and the maximum range of the receiver increased. In the illustrated embodiment the output of the photomultiplier 1 is fed to a variable threshold amplifier 2 the output of which feeds utilization means at 3 and also a pulse repetition frequency counter 4. The output of 4 is a voltage proportional to the number of pulses (noise plus echoes) above the threshold, and is compared in comparator 5 with a reference voltage from 6. The output of 5, representing the difference between the two input voltages, is used at 7 to vary the threshold of the amplifier 2. Alternatively, as shown by connection 8, said output can be used to control the voltages feeding the various electrodes of the photomultiplier 1 whereby the amplitudes of the pulses from the detection are varied. |
