INTRODUCTION TO SONAR 



where a loss in buoyancy with depth exactly 

 equals any gain in buoyancy resulting from a 

 decrease in water temperature or increase of 

 salinity. 



Functional Operation 



To measure sound velocity and to ascertain 

 velocity gradients in the surrounding water, two 

 transducer assemblies (sound heads) are pro- 

 vided with each depth-sound speed measuring 

 equipment. One assembly is mounted on the 

 upper (or sail) portion of a ship. The other 

 device is mounted at the keel. 



To obtain accurate information concerning 

 changing gradients and subsequent effects on 

 buoyancy during diving operations, it is advis- 

 able to use the lower sound head while diving, 

 and the upper sound head while ascending. By 

 following this pattern, radiated heat from the 

 skin of the ship will wash away from the sound 

 head. Radiated heat, consequently, will not inter- 

 fere with measurements of gradients and indi- 

 cations of corresponding buoyancy changes. 



Sound velocity in water is measured in the 

 following manner: The AN/BQH-IA transmits 

 into the water a pulse of acoustic energy. This 

 pulse travels from a transmitting transducer 

 through the water and is received by a second 

 receiving transducer. The time required for a 

 pulse to travel from transmitter to receiver is 

 measured by means of electronic timing circuits. 

 Thus, a direct measurement of sound velocity 

 is made. This method of direct measurement 

 eliminates the need for correlating various factors 

 of the ocean: salt content, density, and tempera- 

 ture, plus pressure corresponding to depth at 

 which velocity is measured. 



Description of Controls 



Operating controls of the AN/BQH-IA depth- 

 sound speed measuring set are described for 

 the recorder and repeater. Refer to figure 5-1. 



• Recorder: Following are the major operating 

 control switches on the recorder. 



1. Power on/off recorder illumination control: 

 This control applies 400-cycle primary power to 

 the recorder. It varies the brightness of the 

 internal chart illumination. 



2. Sound head select: A two-position switch 

 that permits an operator to select either the 

 upper or lower sound head for displaying sound 

 velocity on the recorder drum. 



3. Depth scale select: A two-position switch 

 that permits an operator to select either of two 

 overlapping depth scales. One depth scale is 

 to 800 feet; the other, 700 to 1500 feet. 



4. Press-to-set 4800 fps: A spring-loaded 

 switch, that, when depressed, applies a cali- 

 brating signal internally generated in the partic- 

 ular sound head in use. The switch acts as a 

 system check of performance and accuracy of 

 sound velocity indication. It also assists in 

 proper positioning of new recorder charts. 



• Repeater: The repeater unit is identical to 

 the recorder unit, but the repeater has no 

 operational controls. The only control on the 

 repeater is the power on/off illumination switch. 

 The repeater cannot be operated unless the 

 recorder is also operating. 



Operating Procedures 



Because the AN/BQH-IA and its associated 

 sound heads and depth circuitry are completely 

 transistorized, no warmup time is required for 

 proper operation. Following is the normal oper- 

 ating procedure recommended for the set. 



1. After lighting off the equipment and select- 

 ing the desired soundhead, the recorder illumina- 

 tion control is adjusted to provide sufficient 

 light to clearly view the chart. (NOTE: When 

 surfaced, the upper sound head is not immersed. 

 Care must be taken to avoid energizing this 

 head until the submarine completely submerges.) 



2. The depth scale select switch is set to 

 the desired depth setting (0-800 feet or 700-1500 

 feet). The equipment is now ready for normal 

 operation. 



3. The press-to-set 4800 fps switch is de- 

 pressed and held until the velocity indicating 

 drum reaches a steady position. Indicated veloc- 

 ity position should be 4800 fps. (NOTE: For 

 each sound head the absolute value of the 4800- 

 foot calibrate velocity varies slightly. Test data 

 sheets supplied for the soand head in use should 

 be consulted for exact calibrated readings.) 



4. In the preceding step, when the drum 

 steadies, the press-to-set switch is releaoed. 

 The drum should rotate and indicate the sound 

 velocity in the water at the sound head in use. 



5. When both sound heads are immersed, 

 the sound head select switch may be rotated 

 to select first one, then the other, sound head. 

 Each time the select switch is changed, the 

 drum should rotate to a position that shows 

 the velocity of sound at the sound head selected. 



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