GB604935A - Improvements in or relating to echo-sounders and like sub-aqueous distance measuring devices - Google Patents

Abstract

604,935. Subaqueous audible signalling apparatus. SADIR-CARPENTIER. Aug. 13, 1945, No. 20810. Convention date, June 29, 1944. [Class 118 (ii)] In a submarine echo-ranging device the receiving translator means is resonantly responsive to two markedly different frequencies, one of which is the signal frequency, and the output derived at the second frequency is utilized to control the gain of the output derived at signal frequency so that the gain decreases when the controlling output increases. A note of sonic or supersonic frequency is transmitted and the wave reflected from an obstacle is received by two microphones 1, 2, Fig. 1, of which the first is tuned to the signal frequency and the second to some other frequency. Extraneous noises, which in general have a shock-like effect, cause an equal response in both microphones, but the signal itself has little or no effect on the second mierophone 2. The signal plus noise voltage developed by the signal microphone 1 is passed to an amplifier 3 and hence to a recording or indicating device 4. The noise voltage developed by the noise microphone 2 is detected, amplified and filtered at 6 and a voltage due to the mean noise level is developed across a preferably variable resistance 5 and used as automatic volume control for the signal plus noise amplifier 3. Hence, a high noise level reduces the gain of the amplifier 3 and prevents the noise from producing a spurious indication or record at the end device 4. Delayed automatic volume control may be employed. The signal plus noise amplifier 3 may be a limit amplifier, i.e. may only transmit an output voltage when its input voltage exceeds a given limit, in this case the voltage across resistance 5. Any of these methods may be combined. Instead of two differentlytuned microphones, one magneto-strictive or electro-dynamic microphone may be employed having two resonant frequencies and embodiments of such microphones are briefly described, Figs. 2, 3, 4a and 4b (not shown). The Specification as open to inspection under Sect. 91 describes a method, Figs. 2 and 3 (Cancelled and not shown), in which the signal voltage and the signal-plus-noise voltage are fed in opposition to an indicator device. The purpose of this is not clearly described. This subject-matter does not appear in the Specification as accepted.