ILLUSTRATIONS 



1 Block diagram of the Basic Underwater Sound -Measuring 



System. . . page 6 



2 Basic Sound-Measuring System shown with portable tape 



recorder. . . 7 



3 System noise of the hydrophone -preamplifier. . . 8 



4, 5 Receiving responses of hydrophone M-H90-A, Serial Nos. 1 

 and 6. . . 9 



6 Block diagram of M-H90-A hydrophone with cable and 



connections. . . 10 



7 Diagram of hookup of cable conductors to cable 



connectors. . . 11 



8 Cross talk between calibrate pair and signal pair. . .13 



9 Block diagram of calibrate box. . . 14 



10 Equivalent sound-pressure spectrum level of random-noise 



calibrate signal. . . 16 



11 Frequency-response curves of the portable tape recorder. . . 19 



12 Diagram of two hydrophone suspension systems. . . 22 



13 Spar-buoy type suspension system. . . 23 



14 All-buoyant cable system with shock-cord suspension. . . 25 



15 All-nonbuoyant cable system with a simple float 



suspension. . . 25 



16 Combination buoyant and nonbuoyant cable system with 



shock-cord suspension. . . 27 



17 Simplified all -buoyant cable system. . .28 



18 Nonbuoyant cable system using spar-buoy suspension. . .29 



19 Comparison of noise-spectrum levels for a towed system 



and a slack system. . . 31 



20 Strip-chart records of the one-third octave band levels 



centered at 10, 50, and 1000 Hz, and of the broadband. . . 32 

 Al Block diagram of pressure module and associated ship 



equipment. . . 38 

 A2 External view of pressure module. . .38 



