EQUIPMENT AT MOUNTAIN LAKES 



HI 



^TURNTABLE 



TURNTABLE 



MOTOR 



a GEAR TRAIN 



MANUAL CONTROL 



AC POWER 



ROTATOR 

 SHAFT 



MOTOR 



Fir.iiRK 1G. Schematic of polar recorder servo system. The 5F synchro coupled to the turntable is the director. 1 he 

 thyratron ser\o amplifier controlled l>\ the 5CT synchro furnishes the powei foi the '/t-hp rotatoi dine motor. 



usual range plotted. Plug-terminated patch cords 

 are used in establishing connections to the electronic 

 circuit and the required power supplies. 



Operation of Pulse System 



The pulse system is made up of a pulse generator, 

 transmitter modulator, and a receiver modulator and 

 pulse rectifier which were designed and built by 

 USRL. When used with (he 15-c to 150-kc system, 

 acoustic pulses 0.1 to 30 milliseconds in duration may 

 be produced and recorded. The use of the units is 

 illustrated in Figure 17. A continuous single-fre- 

 quency signal is applied to the input of the trans- 

 mitter modulator, which acts as a "gating circuit." 

 The output of the transmitter modulator is a pulse, 

 that is, a limited train of constant amplitude waves 

 of the signal frequency. The length and recurrence 

 rate of these pulses are controlled by the pulse gen- 



HY0R0PH0NE 



Figure 17. Block diagram of System 2 arranged tor pulse 

 measurements. 



erator. They may be observed and checked on a 

 cathode-ray oscilloscope connected across the output 

 of the modulator. After t hecking, they are amplified 

 and applied through the appropriate connection to 

 the underwater transducer that is serving as a sound 

 source or projector. The nature ol the resulting 

 acoustic signal depends, of course, on the electro- 

 acoustic properties of the transducer. 



The acoustic signal generates in the hydrophone 

 an electric signal that is amplified and applied to the 

 linear or polar recorder attenuator as desired. After 

 further amplification, the signal is passed through 

 the receiver modulator, which is another gating cir- 

 cuit similar to the transmitter modulator. The receiv- 

 ing time can be controlled by the pulse generator in 

 such a manner that any portion of the received signal 

 may be accepted lor measurement and the rest re- 

 jected. To aid in this adjustment, a cathode-ray oscil- 

 loscope is used to observe the incoming signal after it 

 has passed through the receiver modulator. A switch 

 permits the direct comparison of the total signal with 

 the portion accepted lor measurement. This plan 

 allows the elimination of reflections which would be 

 present in continuous-wave measurements and would 

 result in an erroneous signal level. 



If the pulses occur at the rate of 15 per second or 

 more, the pulse rectifier produces a d-c voltage that 

 is suitable for controlling the recorder circuit. 



Units of the Pulsing System 



Pulse Generator. The generator produces the 

 pulses governing the action of the transmitter and 

 receiver modulators. It consists of three unbal- 

 anced multivibrators, A, B, and C, that will produce 



