EQUIPMENT AT MOUNTAIN LAKES 



103 



H 



OSC 3 

 AUXILIARY 



MOD 3 



AUXIUARY 



(C),(D)(E) 



(F) 



(G) 



(H) 



1 USED TO SIMULATE 

 J TEST SIGNAL FOR 



ADJUSTMENT PURPOSES 



NOTE- LETTERS IN ( (REFER TO CORRESPONDING COLUMNS IN TABLE U 



Figure 39. Simplified circuit arrangement using System 2 with auxiliary apparatus lor obtaining a hand-pass tiller 

 adjustable in width up to (i kc and with a mid-band frequency, variable between 3 and 150 kc 



permitting the recorder to run lor an adequate pe- 

 riod with the circuit arranged for broad-band ob- 

 servations. The synchronous motor of the paper drive 

 measures the time of these observations and the paper 

 speed should be at a minimum. 



The circuit arrangement in Figure 40 permits ob- 

 servations on the effectiveness of complex acoustic 

 signals in aural masking. A variety of characteristic 

 sounds on phonograph records is available with 

 which to study masking effects at sonic or supersonic 

 frequencies. 



Operational Studies of Complete Echo- Ranging 

 Systems. With the apparatus connected into a com- 

 plete system for echo ranging, actual trials are made 

 to test the ability for locating small objects in shallow 

 water at distances under 350 meters. A common meth- 

 od is to suspend a small target from a rowboat which 

 travels slowly over the range while the attempt is 



made to locate the target and maintain contact with 

 it. Common targets are 2- and 3-foot hollow spheres 

 and a 4-foot length of 7-inch heavy walled pipe. One 

 of these is suspended from the stern of the boat at the 

 same depth as that of the transducer. Directions for 

 the course of the boat and other communications be- 

 tween operators are carried on by radio telephone. 



The raft has a working space running its full 

 length through the center. The apparatus rests on 

 carriages moving on steel rails the same as on the 

 piers while an overhead rail and hoist facilitates posi- 

 tioning on the carriages. The monorail on pier 1 

 offers the easiest transfer of equipment to the raft, 

 which must be kept level by proper weight distribu- 

 tion. With the gear in place, the raft is located at one 

 end of the range and secured to the shore by 1-inch 

 cables with wide angular spacing. Connections are 

 made to the power and signal lines, which include a 



SYSTEM 2 



WIDE 



BAND 



AMPLIFIER 



FOR DIRECT 

 AUDIO LISTENING 



FOR SUPER- 

 SONIC LISTENING 



\- 



HIGH AND 



LOW PASS 



FILTERS 



ATTENUATOR 



MIXING 

 PAD 



30 A 



TRANSMISSION 



MEASURING 



SET 



ATTENUATOR 



PHONOGRAPH 

 SYSTEM 



r" 



REPRODUCER 



AND 

 PREAMPUFIER 



A 



LOUDSPEAKER 



OR 



1 HEAD PHONES 



Figure 40. Simplified circuit arrangement lor acoustic masking observations. 



