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BELL SYSTEM TECHNICAL JOURNAL 



tories in New York City. In Fig. 2 the transmitter, line, and receiver 

 of the reference system are shown on the three racks at the right. 

 The cahbration apparatus, consisting of an oscillator, thermophone, 

 vacuum tube voltmeter and volume indicator are shown on the other 

 three racks. A schematic diagram of the master reference system is 

 shown in Fig. 3. 



REFERENCE TRANSMITTER 



CONDENSER TRANSMITTER AND ASSOCIATED 4 STAGE AMPLIFIER 



'lS'-- 



CONDENSER 

 TRANSMITTER 



DISTORTION 

 NETWORK 



SECOND 



AND 

 THIRD 

 STAGES 



GAIN 

 ADJUSTMENT 



FOURTH 

 STAGE 



REFERENCE LINE 



VOLUME 

 INDICATOR, 



600 OHM 



ADJUSTABLE 



RESISTANCE LINE 



REFERENCE RECEIVER 



MOVING COIL RECEIVER AND ASSOCIATED 3 STAGE AMPLIFIER 



GAIN 

 ADJUSTMENT 



"UJ 



tiS' 



DISTORTION 

 NETWORK 



THREE 



STAGE 



AMPUFIER 



MOVING COIL 

 RECEIVER 



Fig. 3 — Schematic diagram of master reference system. 



The reference transmitter consists of a condenser transmitter and 

 associated four-stage amplifier. The condenser transmitter is simple 

 and rugged in construction. It has been available for work of this 

 nature for several years during which time considerable experience has 

 been obtained with it. In this system the condenser transmitter is 

 held in an adjustable mounting and is equipped with a guard by 

 means of which the speaker can keep his lips at a fixed distance from 

 the diaphragm. This guard consists of a wire ring 4.7 cms. in diameter, 

 held parallel to and at a distance of 4.1 cms. from the diaphragm of 

 the transmitter by three wire supports. A volume indicator with 

 meter visible to the speaker enables him to maintain an approximately 

 constant talking intensity. In the condenser transmitter," shown in 



6 The theory and operation of this transmitter are discussed in papers by I. B. 

 Crandall, Physical Review, June, 1918, and E, C. Wente, Physical Review, July, 

 1917, and Physical Review, May, 1922. 



