140 



COMPUTATION FROM TEST DATA 



LOG 



QJsiJirlsPlSX/r TTST STATION £__SYSTEM; 



PROJECT «n OOP nATT 12- 2fry<t rnpiF< TO STATION FILE AND N. Y nmrF 2 



_SHEET NO. H_ 



Ficure 4. Sample log sheet covering calibration of QB No. 1 1 1 transducer. 



age was applied to the receiving line from a very low 

 impedance, 0.034 ohm, as shown in (a) of Figure 7; 

 this same voltage was then applied to the receiving 



TRANS LINE 

 £ =135 OHMS 



BATTERY SUPPLY -&- 



T REC LINE 

 CIRCUIT FOR X2=I350HMS 



3A HY0R0PHI 



3A HYDROPHONE 



Figure 5. Circuit used in obtaining reference receiving 

 response chart, 3A89 hydrophone. 



qB *1ll HYDROPHONE 



Figure 6. Circuit used in obtaining receiving response 

 chart, OB No. Ill transducer. 



amplifier through the coupling amplifier, as shown 

 in (b) of Figure 7. The two recorder traces are shown 

 in Figure 8. The log sheet shows that both measure- 

 ments were made with the same receiving amplifier 

 gain. Thus, the difference between the two traces 

 gives the coupling gain or loss. It will be seen that 

 this loss is 6.2 db at 25 kc. 



The generated voltage of the test instrument rela- 

 tive to the voltage of the 3 A hydrophone across 135 

 ohms can now be computed as follows: 



Difference in receiving chart readings +15.2 db 



(From Figures 2 and 3) 

 Coupling loss for test hydrophone +6.2db 



(From Figure 8) 

 Difference in receiving amplifier gain — 4.0 db 



(From Figure 4) 

 Difference in available power to projector ... Odb 



(From Figure 4) 

 Difference in testing distance db 



(From Figure 4) 



+ 17.4 db 



With the calibration of the hydrophone standard 

 (Figure 1) known, the receiving response of the test 

 instrument may be obtained as follows: 



The response of the standard, according to Figure 

 1, is —98.2 db vs 1 volt for a sound field of 1 dyne per 

 sq cm at 25 kc. The response of the test instrument, in 

 accordance with the above computation, is 17.4 db 



