platform transmitted while the surface platform received. Since the SUBSAT equipment in- 

 stallations were quite similar on all four platforms, a single description will be given. 



2.1 SUBSAT EQUIPMENT 



2.1.1 ACOUSTIC SOURCE AND RECEIVER 



The Straza ATM-504A underwater telephone was used as the acoustic source and 

 receiver on all platforms. This unit was already installed on all platforms except the Box L, 

 where a 504A was installed for the DOLPHIN experiment. 



The 504A specifications are shown in Table 3. Basically this unit accepts audio base- 

 band information from 500 to 3000 Hz and converts this to a single sideband acoustic signal 

 appearing between 8.587 and 1 1.087 kHz. Although this unit was primarily designed to 

 operate on voice inputs, the 500- to 3000-Hz range is more than adequate to accommodate 

 the slow-scan format (Table 2). Since the slow-scan signal is essentially a constant-amplitude, 

 frequency-modulated signal it requires a higher duty factor than low-duty-cycle (i.e., high 

 peak to average) voice transmissions. No adverse effects, such as overheating on the 504A, 

 were noted during slow-scan transmissions. Except for a loose edge connector on one of the 

 boards on the Box L, all the 504A units performed reliably. 



TABLE 3. 



STRAZA MODEL ATM 504A ACOUSTIC 

 UNDERWATER TELEPHONE. 



Transmitter: 





Carrier Frequency 



8.087 ±1 kHz 



Upper Sideband Passband 



8.587 to 11.087 kHz ±3 dB 



Baseband Passband 



500 Hz to 3 kHz 



Acoustic Output 



100 W, 25 W, 10 mW, selectable 



Source Level (Conical) 



203dBre 1 ,uPa at 100W 



(Omni) 



196dBre 1 uPa at 100 W 



Receiver: 





Frequency Response 



8.587 kHz to 11.087 kHz 



Sensitivity (Conical) 



+70 dB re 1 juPa 



(Omni) 



+74 dB re 1 /iPa 



Audio Bandwidth 



500 Hz to 3000 Hz ±3 dB 



Weight, Size and Power: 





Weight 



37 1b 



Overall Dimensions (inches) 



5 .2 high by 1 9 wide by 1 5 .4 deep 



Input Power: (Far Mode) 



490 W 



(Med. Mode) 



220 W 



Except for the Box L boat, all platforms had the option of using either the hull-mounted 

 conical or omni transducers. On the Box L boat a SP23LT conical transducer was lowered 

 and used for receiving at a depth of 200 ft. A painted plywood baffle was mounted to the 

 rear of this transducer. Both the 200-ft depth and baffle were selected to minimize the entry 

 from above of surface-reflected sound to the rear of the transducer. The beam pattern of 

 the baffled conical transducer is shown in fig. 1. 



