Patent GB-635337-A (GB)
Title: Improvements in and apparatus for submarine echo ranging
IPC: G01S15/10
Filed: 1944-10-27
Abstract: 635,337. Echo sounding and distancemeasuring apparatus. SUBMARINE SIGNAL CO. Oct. 27, 1944, No. 21022. Convention date, Jan. 20, 1940. [Class 118 (ii)] In submarine echo ranging the wave-form of the transmitted compressional wave pulse is continuously and periodically varied in frequency, and the receiver includes a detector responsive only to the frequency variations. A circuit suitable for such a detector comprises diodes 61, 62 (Fig. 9), connected as shown to a transformer 63 whose primary and secondary windings are tuned by condensers 65, 64 to the mean signalling frequency. At this frequency, the sum of the rectified voltages applied across the resistors 68, 69 is zero, but when oscillations of a frequency off resonance are applied a resultant voltage of polarity and magnitude dependent on the difference between such frequency and the resonant frequency will be obtained. By using a signal of ultrasonic frequency, and by varying this frequency at a sonic or ultrasonic rate, the echo pulses will appear as a corresponding sonic or ultrasonic output from the detector which may be applied to earphones or other indicating means whereby the echo time may be determined in the normal way. Transmitter.-Fig. 2 shows circuits for producing suitable signal pulses: the inductance of the grid circuit of the vacuum tube oscillator 8 is varied to produce the required frequency variations by varying the permeability of the core 3 of the coil 6; to do this, the flow of direct current through magnetically-opposed coils 4 and 5 connected in series with the secondary of a transformer 35, is controlled by a vacuum tube oscillator 37; the frequency of the latter oscillator may be constant, being set by adjustment of the tuning condenser 38, or continuously varying, being controlled by the motor-driven tuning condenser 19, or may be changed by the use of circuits as described in Specification 635,338; keys 42 and 15 may be controlled by a relay arrangement such as that described in Specifications 635,333, and 635,334. After passage through amplification stages and a current limiter to ensure uniform amplitude, the output of the tube 8 is applied to a compressional wave transmitter, e.g. of the Rochelle salt type. Receiver.-In addition to a compressional wave receiver (the transmitting unit may.serve for this purpose), a differential detector as described above, an indicator, and suitable amplifiers, the receiving system may include a current limiter (which, in conjunction with a local generator for injecting a constant signal of mean frequency, eliminates unwanted amplitude variations), band filters inserted both before and after the detector, a rectifier and local heterodyne oscillator for changing the frequency, and a frequency multiplier for extending the limited frequency band, which may conveniently be covered by compressional waves, to the full optimum frequency range of the detector. When the oscillations of the tube 37, Fig. 2, and therefore of the differential detector, Fig. 9, are of ultrasonic frequency, the output of the latter may be heterodyned with a locally-generated signal to produce oscillations of sonic frequency applicable to the earphones &c. The current limiter may comprise a circuit including a tetrode vacuum tube so arranged as to be operated slightly below the saturation point of the plate characteristic when no signal is present.