GB493340A - Improvements in and relating to the determination of the direction of incidence of oscillatory phenomena - Google Patents

Abstract

493,340. Locating sounds and like vibrations ; directive wireless systems. TRIGGS, W. W. (Akt.-Ges. Brown, Boveri, & Cie) Dec. 1, 1937, No. 33192. [A Specification was laid open to inspection under Sect. 91 of the Acts, June 2, 1938.] [Class 118 (ii)] [Also in Group XL] The direction of incidence of oscillatory phenomena, such as sound or electromagnetic oscillations is determined by using spaced pick-up devices to generate electric potentials which are combined by mutual modulation to produce a control potential varying in accordance with the phase difference existing between corresponding components of the same frequency reaching the pickup devices. Thermionic amplifiers may be used and the input may be heterodyned, preferably using a common oscillator. Two receivers S1, S2 which, if sound is being received, may be microphones, feed alternating voltages to amplifiers VI, V2, the gain of which is automatically controlled through rectifiers Rl, R2 having square law characteristics. Retarding devices L1, L2, inserted to give a phase shift so that the output voltages are in phase, may comprise a magnetizable steel band moving past recording and receiving heads or a time lag may be inserted using an acoustic or electrical system. Variable filters Fl, F2 pass suitable frequencies, low frequencies being used when searching and higher frequencies for fine adjustment. Further amplifiers V11, V<1>2 feed a modulator M, which, since the inputs have the same frequencies gives a D.C. output, that is fed through a low pass filter B to a direct current meter J giving a maximum indication when the time lag introduced by L1, L2, causes the voltages applied to M to be identical. A.C. instruments Z1, Z2 indicate the voltage levels being used and by combining their indications with that of indicator J, the amount of disturbance due to other sources may be seen. In a modification, the retarding devices L1, L2 are omitted and the receivers S1, S2 are mounted on a beam which is rotated to be perpendicular to the direction of the source, the vibrations then arriving in phase at the receivers. In another modification, Fig. 7, an oscillator O modulates the phase-corrected input voltages supplied to modulators H1, H2 the filters P1, P2 passing one of the side bands to the main modulator M. In such an arrangement, condenser microphones, in which a carrier is applied instead of a constant bias, may be used, modulators H1, H2 then being unnecessary. In a further modification, Fig. 9, the voltages appearing at 13, 14 are fed through M1, B1, J1 corresponding to M, B and J, while a second chain M2, B2, J2 is fed with voltages derived from the same point 14. The difference in the readings of J1, J2, is shown by indicator J. When searching, adjustments of the receivers &c. are made to get a maximum indication on J2, this operation serving as a coarse adjustment. Further adjustment making the inputs to 13, 14 identical, causes J1 to give a maximum while the reading given by indicator J falls to zero. Two receivers may be used, each of which is sensitive in one plane, so that a hornless arrangement such as a number of microphones on a straight beam may be used, or a single microphone having a cylindrical sound sensitive surface may be employed. To reduce disturbances due to pulses of high intensity amplitude limiting devices may be used.