APPENDIX C 



EXPERIMENTAL EQUIPMENT AND DATA REDUCTION 



1. EXPERIMENTAL EQUIPMENT 



On the USNS Charles H . Davis, two projectors were combined in one unit to 

 cover all three frequencies . The serial numbers and the individual sensitivities* 

 are listed in Table C-l . The input currents to the projectors were recorded 

 during the experiment and used to determine the radiated acoustic source level. 

 In analysis, it was assumed that the source level was unaffected by tilting or ro- 

 tation of the hydrophones . 



On the receiving ship, the USS Rexburg, three hydrophones were suspended at 

 50 feet, 90 feet, and 300 feet. Their sensitivites* are presented in Table C-l . 

 The hydrophone outputs were recorded simultaneously on magnetic tape and (at 

 one frequency only per channel) on Visicorder paper . A block diagram of the 

 recording system aboard the Rexburg is shown in Figure C-l . Calibration sig- 

 nals were injected into the three hydrophone channels by a calibrated local os- 

 cillator and attenuator loaded by a low resistance in series with the hydrophone. 

 The use of the calibration voltages is discussed in the next section. 



A radio pulse, synchronized with each of the acoustical pulses, was transmitted 

 from the Davis to the Rexburg where it was recorded on Channel 7 of the mag- 

 netic tape. Clock pulses at 5-second intervals were recorded on tape Channel 9. 

 Radio telephony signals from the Davis were recorded on tape Channel 14. Fre- 

 quently the signals on Channels 7, 9, and 14 interfered with the hydrophone out- 

 puts on Channels 1, 2, and 3 and added to the complexity of subsequent data 

 analysis . 



2. SYSTEM CALIBRATION 



As described in the preceding section the output of each hydrophone was recorded 

 on two channels on the magnetic tape . The signals were recorded continuously 

 in each channel regardless of frequency. At the end of each of the six runs, an 

 electrical calibration signal of suitable voltage was injected into each channel of 

 the receiving system and recorded. These calibration signals were at 3000 cps 

 on Channel 1, 1300 cps on Channel 2, and 700 cps on Channel 3. We will identify 

 these particular frequencies, one appropriate to each channel, by the symbol f Q . 

 The magnitude of the calibration signals was voice -recorded on the magnetic tape. 



The calibration curves were provided by USNEL Transducer Calibration 

 Facility. 



C-l 



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