72 



USRL TEST STATIONS 



HETERODYNE OSCILLATOR 



DETECTOR 



TUNING 



OSCILLATOR 



678 KC 



VARIABLE 



FREQUENCY 



OSCILLATOR 



650 TO 500 KC 



(650— f ) 



FIXED 

 FREQUENCY 

 OSCILLATOR 



650 KC 



MODULATOR 



BUFFERS 

 AVC CIRCUIT 



ATTENUATOR 

 650-(650-f) 



-BROKEN LINES INDICATE ALTERNATE 

 CIRCUIT ARRANGEMENTS 



THYRATRON 

 CONTROL 



AMPLIFIER 

 26 KC 



)L 



I2C BAND 

 PASS FILTER 

 CENTERED 



(678—650) 

 KC 



MODULATOR 

 (650 -f*+f 



28 KC DETECTOR CIRCUIT 650 KC 



._T L 



TUNING 

 INOICATOR 



CATHOOE 



RAY 



OSCILLOSCOPE 





AUDIO 

 AMPLIFIER 



AND 

 MONITOR 

 SPEAKER 



---J 



WIDE 



BAND 



AMPLIFIER 



001 TQI50KC 



30 A 



TRANSMISSION 



MEASURING 



SET 



■BALANCED COAXIAL TRANSMISSION LINES" 

 BETWEEN LABORATORY AND PIERS 



17, 



ER RECEIV- 



IMPEDANCE MATCHING 



COILS, PAOS.AND 



WATTMETER CIRCUIT 



SWITCHING CIRCUIT 



Lb= 



7& 



IRCUIT . 



,2 LINES 

 r AVAILABLE 



NG BOOTH 



COUPLING AMPLIFIER.DC 



SUPPLY CCTS , CALIBRATION 



SIGNAL CIRCUIT 



SWITCHING CIRCUIT 



L L 



.- BALANCED COAX LINE BETWEEN PIER BOOTHS 

 m BALANCED COAX LINES BETWEEN PIER 800THSAND TEST AREA TERMINAL BOXES- 



7.7. 





TERMINAL 

 BOX 



TO PROJECTOR 



FROM HYDROPHONE 



Figure 6. Block diagram of 15 c to 150 kc S)stcm 1. 



thermal noise source. Two band-pass niters limit the 

 frequency spectrum to 650 ±0.15 kc or 650 ± 3 kc, as 

 desired. These signals are used to replace the fixed 

 650-kc signal in the heterodyne oscillator. The final 

 signal output is then a band of thermal noise 300 c or 

 6,000 c wide, centered at the frequency given by the 

 oscillator setting. 



The noise output should be at least 10 db below the 

 single frequency output to prevent peak clipping in 

 the modulator circuit. This adjustment is made by 

 controlling the output of the noise generator circuit. 



The midpoint of the noise band in this generator 

 is 650 kc for correct frequency alignment of the out- 

 put band. The frequency range of the variable oscil- 

 lator must be exactly 650 kc to 500 kc. To obtain this 

 condition, adjustments are made on the generators as 

 follows: The noise generator circuit, functioning 

 only as an amplifier, is sharply tuned by a filter 20 c 

 wide centered at 650 kc. This is connected between 

 the fixed-frequency oscillator and the following mod- 

 ulator. The fixed oscillator is then tuned for maxi- 



mum output at any convenient frequency setting. 

 With the frequency of the fixed oscillator thus estab- 

 lished at 650 kc, the frequency scale is aligned at 60 c 

 and 100 kc by adjustments on the variable oscillator. 



Power Amplifiers 



Power amplifiers with a maximum gain of 40 db 

 are associated with each system. The maximum undis- 

 torted power level of system 1 is 177 db and that of 

 system 2, 173 db, but an auxiliary amplifier, described 

 later, may be used with either system to reach an un- 

 distorted level of 192 db vs 10 _lli watt, or about 1,500 

 watts. 



System I , covering the range from 15 c to 150 kc, re- 

 quires two output transformers for its power ampli- 

 fier. Automatic transfer between them is effected near 

 2 kc by a switching circuit operated by a cam on the 

 oscillator frequency dial. System 2 employs two power 

 amplifiers, covering ranges from 15 c to 30 kc and 

 from 300 c to 150 kc. The amplifiers of both systems 

 have been designed to operate into a load impedance 



