560 



BELL SYSTEM TECHNICAL JOURNAL 



for changing the ampHtude, one of which varies the grid potential of a 

 vacuum tube which acts to limit the current supplied the driving coil, 

 and the other, a variable capacitor in the cireuil containing the 



Tr" 



THERMOSTAT 



PICK-UP 

 COIL 



FREQUENCY_^ 

 ADJUSTMENT 7f- 



W/; 



DRIVE 

 COIL 



Y 



rx 



\^z^=,.zsrz^z^,z:^-^' 



Fig. 7 — Carrier and motor control oscillator. 



pick-up coil varies the phase relation between the currents in the 

 drive and pick-up coils. Three outputs are provided from the oscilla- 

 tor, two for the sending and receiving motor control circuits and the 

 third for the carrier frequency supplied the sending light valve. 



