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OUR PHYSICAL WORLD 



currents than the ordinary telephone transmitter. While this 

 method of using the microphone in the antenna circuit is possible 

 within very narrow limits of current strength, it is not practical. 

 The reason for this impracticability is that large current strength 

 in the antenna circuit is necessary for long-distance transmitting 

 and broadcasting of lectures and musical programs. 



-plate voltaic > < -filament voltage- 



01 



FIG. 128. The radio telephone transmitter: (/) telephone transmitter; 

 (tr) telephone transformer; (m) modulation tube; (0} oscillating tube; (/ x , 1 2 , /a) 

 inductances; (c 8 ) fixed condenser; (a) antenna; (g) ground. 



In order to produce this sound modulation in large radio 

 telephone transmitting stations, recourse is again had to the 

 vacuum tube. When used for this purpose, it is called a modu- 

 lator. The connections for this use of the vacuum tube as a 

 modulator in a radio telephone transmitting circuit are shown 

 in Figure 128. 



By a study of this diagram (Fig. 128) it will be noted that one 

 tube (o) is connected into the circuit as a generator of continuous 

 waves. The telephone transmitter or microphone (/) is con- 



