Patent GB-758881-A (GB)
Title: Improvements in or relating to echo sounding systems utilising non-linear recording amplifiers
IPC: G01S15/96
Filed: 1954-06-01
Abstract: 758,881. Echo-sounding. ATLAS-WERKE AKT.-GES. June 1, 1954 [June 1, 1953; July 21, 1953], No. 16205/54. Class 118(2) To avoid confusion of echoes from closely situated objects (for example, a shoal of fish and the seabed, or a pocket of mud and the seabed proper), when recording on electro-sensitive paper use is made of the difference in amplitude of such echoes. Due to the unfavourable graduation characteristic of the recording paper small differences in echo amplitude record as equal intensities of blackening when linear amplification is employed, but provision is made for limiting weaker echoes to a level which does not record as full black while ensuring that stronger echoes always record as full black. In the embodiment shown in Fig. 2, echo signals from a transducer 14 are fed to an amplifier 11, the output from which is fed to two parallel potentiometers 20 and 21. These feed a further amplifier 12 through a voltage' limiter circuit 23 and a bottom clipper circuit 32, respectively, each comprising biased diodes in reverse parallel connection. The biasing potential of the circuit 23 is preferably a few volts, and that of circuit 32 equal to or larger than this value. The output from amplifier 12 is fed to a stylus 16 to mark recording paper 17 passing over a platen 18. The gain of amplifier 12 is set once and for all such that the recording current produced when maximum signal permitted by the voltage limiter 23 is being received gives a grey shade, as distinguished from complete blackening. of the paper. The slider of potentiometer 20 is then pushed upwards till the noise level prevailing at transducer 14 just produces feeble recordings not sufficient to impare he distinctness of echo signals. Thus high sensitivity is obtained without blackening of the paper. Strong signals such as from the seabed, however, will cause current to pass circuit 32 and may record as complete blackening. The transition range is controlled by potentiometer 21. Amplifier 11 has linear amplification up to the amplitude of the sea bottom echo. Amplifier 12 may limit its output at a value slightly above that required for complete blackening to avoid damage to the recording paper and smoking, irrespective of the setting of potentiometer 21. In an alternative embodiment (Fig. 3, not shown), the signals from transducer 14 are fed to two similar superhet amplifiers whose outputs are jointly fed to the recording device. The inherent saturation outputs of these amplifiers are somewhat above the value required to give complete blackening of the recording paper. One amplifier, however, has its output degraded by suitable insertion of a resistor, or by reduction of screen voltage on its output valve, so that only recordings in a grey shade are produced; the gain control 'of this amplifier is set high for optimum sensitivity. The gain control of the other amplifier (capable of full black recordings), is set so that only strong echoes, such as from the sea bottom produce full black. A further embodiment suitable for the special case of mud deposits comprises two separate transducers functioning at different frequencies (Fig. 4. not shown). Two sounding pulses of 80 Kc/s and 15 Kc/s are emitted simultaneously-the former giving an echo off the mud layer but failing to penetrate to the solid sea bed, whilst the latter gives an echo from the solid bottom but negligible reflection from the mud layer. The respective echoes are received by tuned transducers connected to amplifiers as in the previous embodiment, the strong 15 Kc/s sea bottom signals pass through an amplifier set at low gain and produce black recording while the weaker 80 Kc/s mud signals are greatly amplified but limited to produce a grey shade only. Instead of transmitting the pulses of different frequency simultaneously they may be emitted in succession at the beginning ,of travel of the stylus over the recording paper. The invention may be used generally for distinguishably recording any two kinds of echo signals which may be separated by their properties. For example, echoes arriving from different directions may be separated by directional transducers