GB1394985A - Control arrangements for own doppler nullification in sonar systems - Google Patents

Abstract

1394985 Sonar systems PLESSEY CO Ltd 22 Aug [1968 [9 June 1967] 26754/67 Heading H4D A conventional sonar system (Fig. 1, not shown) carried by a ship 6, Fig. 2, and generating a signal having a frequency dependent upon the relative velocity of a target 7 with respect to the ship includes a control arrangement for nullifying the Doppler effect due to the ship motion, this arrangement generating a control voltage proportional to the quantity V T COS# T +V R COS# R where V represents the ship velocity, # represents the angle between the direction of ship travel and the line of sight with the target and T and R represent the values of V and # at the instants of transmission and reception, respectively, of the acoustic signal. The control voltage is used to modify the frequency-dependent signal to produce a resultant signal having a frequency dependent upon the absolute velocity of the target. As shown in Fig. 3, the receiver mixer 8 receives a sonar signal from a submerged transducer and also a signal from a second mixer 9, the mixer 9 having a fixed frequency input and also a correcting frequency input derived from own Doppler nullifier computer 11. The computer 11, Fig. 4, for deriving VTCOS# T + V R COS# R , comprises a V T V R servo 12 generating an A.C. voltage proportional to the ship's speed, this voltage being fed to the stator windings of three synchro resolvers 13, 14, 15. The three resolvers correspond with three channels related to three 30 degree sectors covered by the sonar, i.e., a centre sector and left and right hand sectors adjacent the centre sector. The rotors of the resolvers 13, 14, 15 are ganged together and rotated by a # T # R servo 16 through the angle #, the power being derived from the ship's gyro compass. The A.C. outputs from the resolvers are proportional to Vcos# and are fed to phase conscious rectifiers 17, 18, 19 which generate D.C. outputs having levels proportional to Vcos#. The outputs from rectifiers 17, 18, 19 are fed via T/R switches 20, 21, 22 to a respective memory device 23, 24 or 25 during transmission or a respective amplifier 26, 27 or 28 during reception, the outputs from 23... 28 being continuously added in devices 29, 30, 31. Thus the quantity V T COS# T +V R COS# R is derived separately for each channel and is fed to the voltage controlled oscillator 10 related to that channel.