Recognizing the problem, the engineers of the Harvard Un- 

 derwater Sound Laboratory set to work to design apparatus which 

 could conveniently measure the transmitting and receiving per- 

 formance of echo-ranging equipment, thus enabling the gear to 

 be tune 1 and adjusted, tested for operational deterioration 

 and critically compared with other sonar equipment. 



Sound Gear Monitor . 



A solution to the problem of developing a device which 

 determined receiving and transmitting directivity patterns 

 aboard ship was found in a portable apparatus known as the 

 Sound Gear Monitor (SGM) or in Navy terminology, the Under- 

 water Sound Portable Test Equipment,, 



With this equipment it was possible to measure the trans- 

 mitting and receiving frequency response characteristics of 

 sonar gear, the transmitting and receiving directivity char- 

 acteristics and the approximate transmitted power and receiving 

 sensitivity In each application the monitor made a direct 

 measurement of the over-all response of the sonar system,, Thus 

 the transmitting function of a sonar system was tested by meas- 

 uring the sound pressure which the projector produced in the 

 water, and the receiving function was tested by evaluating the 

 response of the system to an underwater sound signal of known 

 property „ 



Tests showed that two portable Sound Gear Monitors were 

 all the equipment necessary to make simple response pattern 

 measurements of sonar projectors „ While testing a projector 

 in transmission, one sound gear monitor was used to energize 

 the projector. The second monitor was used as in normal 

 service to receive the sound energy emitted by the projector 

 under test. In testing the receiving function of a projector, 

 the transmitting and receiving roles of the two monitors were 

 interchanged by their respective panel switches „ 



Once placed in service, the Sound Gear Monitors imme- 

 diately proved their usefulness. They disclosed a dismaying 

 situation with respect to existing echo-ranging gear on some 

 Navy vessels. 



Thus while testing with the monitor on the destrovers 

 USS DAELGREN and USS NIELDS, the Harvard scientists dis- 

 covered that apparently because the vessels were fitted with 

 streamlined domes enclosing the projectors, installations 



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