EQUIPMENT AND FIELD PROCEDURES 



275 



MATCHING TRANS- 

 FORMER ATTENUATOR 

 a PREAMPLIFIER 



ATTENUATORS WITH 

 ELECTRONIC CONTROL 



AMPLIFIER AND 

 ISOLATION STAGE 



STROBOTRON TIMER 

 FORK CONTROLLED 



STROBOTRON TUBE 



NEON LAMP 



RECORDING CAMERA 



FiGtjRE 3. Schematic 



ic arrangement of apparatus in system used recently at San Diego (equipment C of text). 



msec. During the interval 50 to 70 msec, the signal 

 level gradually rose to its fully steady state value, 

 which was maintained for times greater than 70 msec. 

 With the QCH-3 equipment A, the smallest re- 

 cordable reverberation level was usuallj' limited by 

 the level of amplifier noise. On occasion, in noisy 

 areas, the ambient water-noise level exceeded the 

 amplifier-noise level. 



Equipment B 



This equipment was devised for use with the QB 

 crystal transducer. Since the QB was used both as a 

 projector and as a receiver, the electronic setup had 

 to be somewhat different from the equipment de- 



scribed under equipment A . A changeover relay had 

 to be provided to switch the transducer from the pro- 

 jector circuit to the receiver circuit. An improved 

 power amplifier was built for this system, with the 

 result that the projected signal was nearly square- 

 topped in form. Since the receiver circuit is not con- 

 nected while the projector circuit is in operation, no 

 blocking during the interval of projection was en- 

 countered in this system. Even though the receiver 

 circuit is not connected during the ping, a record of 

 the outgoing ping is obtained on the film which re- 

 cords the reverberation; this "ping record" is due to 

 the electrical cross talk generated in the receiver cir- 

 cuit by the high voltages in the projector circuit 



