Patent GB-296762-A (GB)
Title: Improvements in or relating to signalling systems for giving audible signals
IPC: G01S1/72
Filed: 1928-09-06
Abstract: 296,762. Blondel, A. Sept. 7, 1927, [Convention date]. Navigable channels and courses, systems of indicating; determining bearings acoustica!ly.- In apparatus for emitting submarine or aerial sound signals of the kind wherein a number of spaced sound emitters arranged in a straight line, produce a concentration of sound at a great distance about a line perpendicular to that of the sound emitters, provision is made whereby such zones of maximum or minimum sound intensity resulting from interference are automatically and continuously oscillated about a mean position constituting the line which the navigator is to follow. Such oscillation may be produced in many ways. For example, Fig. 1 shows seven sound emitters A1 - - A7 arranged in line and spaced apart at a distance of half a wave length. The line OX of maximum intensity of sound is oscillated between OY1 and OY2 by imposing on the different emitters differences of phase which increase or decrease regularly from one to the other and ame varied alternately in the two directions. Directions to right or left of the line OX are distinguished by modifying the note of the emitters at the moment of passing through OP so that the note is higher on the side Y1 than on the side Y2. Moreover, a characteristic signal may be emitted at the extreme positions OYl, OY2. The generators G1 - - G4 are coupled between and actuated by the same motor M, and the variations of phase may he effected by means of the differential gears I between the generator rotors, the planet-wheel carriers being continuously oscillated about a mean position by motor m1 through rods and cranks F, H. Alternatively, Fig. 7, the alternators G1, G2 for the emitter system A1, A2 are constructed with movable stators adapted to be oscillated by means of pinions E, E2 and motors m1, m2. In a modification, Fig. 8, the diaphragm emitters are replaced by two compressedair sirens S1, S2 of the rotating drum type actuated by synchronous alternating-current motors M1, M2 displaced by half a period with respect to one another and provided with movable stators which are oscillated bv means of a motor m3 and gears T1, T2, a movable contact C actuating the relays D1, D2 which reverse the excitation of the motor m3. The intensity of emission may be varied bv valves. To avoid disturbances arising from reflection of the waves from a shore on the side opposite to the direction of signalling, reflecting surfaces RR, Figs. 1 and 7, of metal or masonry may be installed at a distance of half a wave length from the emitter. In other modifications the emitters are grouped along two different lines. For example, Fig. 2, the emitters A1- A6, grouped along the line UU, are excited in such a manner that the sound beam produced is of opposite sign to that produced by the emitters B1 - - B6, grouped along the line VV. The amplitude of the vibrations emitted bv one group of emitters is regularly varied from zero to a positive maximum while that emitted from the other group is varied from the maximum to zero, the emission being zero in the direction OP1 at the moment when it is a maximum in the direction OP2, and the line of silence OX swinging to right and left of its mean position. In a further modification, the displacement of the phases of the alternators is obtained by arranging all the armatures in the same angular position and suitably displacing the inductors. Specification 239,513 is referred to.