Table 3. — Specifications of SM506 sonar system 



Projector 

 Source frequency 

 Source level 

 Horizontal beam width 

 Vertical beam width 



Receiving hydrophone 

 Horizontal beajn width 

 Vertical beam width 

 Open circuit sensitivy 



CTPM ranges 



Horizontal scan rate 



Presentation CTM 



7-inch plan position indicator scope 

 5 -inch "A" type display on CRT 

 Audio 



Presentation CTD 



7-inch relative bearing display 

 5-inch frequency spectrum display 

 Audio 



60-75 kHz, 70 kHz in CTD mode 

 +95 db re it bar/volt 1 yd, 

 20° 

 20° 



4° 



10°, 20° 



- 75 db re 1 volt/// bar 



100, 200, 4-00, and 800 yds. 



25°/second on 100, 200, and 400 yds. 

 10°/second on 800 yds. 



Data storage 



Video, audio, range, servo, and mode information to multiplexer and Ampex 

 Model SP-300 tape recorder. Playback through system. 



frequency analyzer of higher resolution, per- 

 mitted our sonar to be used to locate and also 

 classify a target. The system components 

 were packaged to mount on vessels of con- 

 venience; the underwater unit was mounted 

 on an over-the-side column. 



Methods 



When a fish school was located, the CTFM 

 mode was used to position the boat 100 to 200 

 yards (91.4 to 182.9 m.) from the school. If 

 the school was moving we tried to match its 

 velocity and direction of movement with the 

 vessel. When the school was positioned, the 

 sonar scan was locked and the system placed 

 in the CTD mode. In this mode a continuous 

 70 kHz tone was transmitted fronn the sonar 

 projector. The echo of this tone plus Doppler 

 infornnation was received by the hydrophone, 

 mixed and filtered to remove the portion 

 corresponding to 70 kHz, and fed to the 

 spectrum analyzer. The spectrum analyzer had 

 a DELTIC to raise the Doppler-frequency 

 information by factors of 2 or 4 by lO"' and 

 allow frequency resolutions of 3.33 Hz or 1.67 

 Hz over a band of ± 600 Hz or + 300 Hz. The 

 Doppler spectrum could be displayed on a 

 CRT and photographed or recorded on magnetic 



tape, or the same information could be stored 

 and displayed repeatedly on the CRT by locking 

 the DELTIC. 



The incoming signal was sampled by logic 

 circuitry to convert Doppler-frequency infor- 

 mation into digital form. This digital 

 information was loaded into the delay line at 

 the rate of 100 ^ sec. /bit when the + 600 Hz 

 Doppler band was used and at 200 // sec./bit 

 when the t 300 Hz band* was used. Since the 

 DELTIC could store 3,000 bits of information, 

 the initial loading time of the analyzer was 0.3 

 sec. or 0.6 sec., depending on the resolution 

 selected. After the line was loaded, new 

 Doppler information could be added and old 

 information dropped at the rate of about one 

 bit/150 n sec. The output of the analyzer then 

 was analogous to a photographic time exposure 

 of the Doppler data received in a 0.3- or 

 0.6-sec. interval. The analyzed Doppler infor- 

 mation was presented as video on the CRT 

 at 5 sweeps per second. Frequency was 

 displayed along the horizontal tinne line with 

 center frequency (no Doppler) at the center 

 of the scope, up -Doppler to the left, anddown- 

 Doppler to the right (fig. 13). Vertical deflection 

 depends on the number of times a particular 

 frequency was present during the load time of 

 the delay line. A single frequency was shown 

 as a single high spike, whereas multiple 



15 



