Patent GB-633352-A (GB)
Abstract: 633,352. Course recording apparatus. SUBMARINE SIGNAL CO. Oct. 4, 1946, No. 29616. Convention date, June 15, 1943. [Class 97 (ii)] [Also in Group XXXV, XXXVIII and XL (c)] In an echo-ranging system preferably employing compressional waves for the detection of submarines, the relative positions of an object and the course of the observing vessel V are plotted. An oscillation of 12,500 cycles is produced, amplified and amplitude modulated over a continuously varying range of 100 to 200 cycles and is projected by magnetostriction, piezoelectric or dynamic means 1. A directionally sensitive receiver 8 is rotated at a constant rate and any reflected wave is picked up and one side-band is extracted, amplified and heterodyned with the modulating oscillator frequency. This signal is heterodyned with a fixed oscillation to provide a low-frequency output of the order of 100 to 200 cycles, such that the frequency represents the distance of the object, with only a small error due to the Doppler effect caused by relative motion between object and vessel. The apparatus for utilizing this signal comprises a truck 26 freely mounted on rails 29 and carrying an upper truck 27 on rails 30. This truck 27 carries a motor 63 which is energized in accordance with any change of heading of the vessel to rotate a small carriage with a wheel 35 that is pressed in contact with a fixed cork surface 36 by three springs 59. The wheel 35 is driven through gearing 44, 43, 41, 42 by a motor 45 which is energized in accordance with the speed of the vessel, so that the truck 27 imitates the movement of the vessel. Mounted on the truck 27 is a motor 81 which rotates a circular platform 83 in synchronism with the rotation of the receiver 8 and this platform carries annularly arranged permanent magnets 84 and slip rings 85 engaging brushes 86. Above the platform 83 is a fixed non-magnetic plate 89 carrying a sheet of recording paper 90 on which slides a ring 92 having spaced armatures 110 which cause it to follow the movements of the platform 83 and magnets 84. A bar 94 is mounted by springs 95, 96 on the ring 92 to permit vibration about a horizontal axis and carries reeds 97 tuned to various frequencies in the range 100 to 200 cycles. This bar 94 is vibrated by an armature 101 and an electromagnet 98 on the platform 83, this electromagnet being energized by the demodulated signal from the receiver 8. When a reed vibrates sufficiently, the paper is marked by a current flowing through it to the plate 89 from the reed and a lead 91<SP>1</SP>. In a modification, Fig. 7, current is fed to the reeds 97 and to a central stylus 107 recording the vessel's course, through a rectifier 103 from a transformer 99, 100, the other side of the winding 100 being connected to the paper 90 through a large surface contact of the ring 92. A reed which produces a mark is spaced from the stylus 107 by a distance corresponding to the delay of the reflected signal and the reed lies momentarily in a direction corresponding to the momentary direction of the receiver 8. The windings 100, 99 are mounted in juxtaposition on the ring 92 and platform 83 respectively. When the ring 92 reaches the edge of the paper it contacts a fence 93, thereby energizing a relay 113 which in turn energizes a solenoid 74 and raises the wheel 35 off the surface 36. Springs 76, 77, 78, 79 then centre the apparatus and a fresh sheet of recording paper is drawn into place by a motor, also energized by the relay 113, Fig. 4 (not shown). In addition to detection of unknown objects, the apparatus may be used for automatically plotting the area surrounding the vessel as it moves through the water. The transmitter 1 may operate continuously or only for a given time interval.