614 BELL SYSTEM TECHNICAL JOURNAL 



100 volts at the high frequency motor. The power taken by the d-c. 

 motor was approximately .8 ampere at 110 volts. The current 

 through the regulating field controlled by the 17.7-cycle circuit was 

 of the order of 20 to 40 milliamperes at 100 volts depending upon 

 the phase position at which interlock occurred. It was found prefer- 

 able to cut off the low frequency interlock feature after synchroniza- 

 tion and framing had been obtained in order that irregularities in 

 the time of contact closure of the relay might not produce changes in 

 field strength of the d-c. motor which in turn would cause irregularities 

 in power output. Such irregularities would give rise to phase shifts 

 in the high frequency machine, thereby producing unsteadiness of 



the picture. 



Operation on Radio Channel 



In the case of transmission of the synchronizing current by radio 

 instead of by wire the same apparatus is employed except that it 

 was found necessary to use a much higher value of high frequency 

 current in order to hold the high frequency motor in step, the current 

 being approximately 4 amperes as compared to 1.5 amperes in the 

 case of the other motors. This greater current was found to be 

 necessary in order to hold the motor in step within the necessary 

 phase angle of displacement, in spite of various types of interference 

 picked up by the radio receiver, and associated circuits. This was 

 mainly inductive interference from the picture and speech trans- 

 mission sets arising from the fact that the synchronizing current was 

 transmitted from New York to Whippany and picked up on a re- 

 ceiving set there, whereas the picture and voice current was trans- 

 mitted from Whippany to New York. A certain amount of inter- 

 ference was also encountered from ship spark sets and static. 



Speed Regulation of Transmitting Motor- Generator 

 As previously explained under "General Requirements" the essential 

 requirement of the speed regulator at the transmitting end is to limit 

 the acceleration to about one revolution per second per second, over 

 intervals as small as .01 second. The ordinary type of centrifugally 

 operated vibrating contact regulator keeps the motor continually 

 accelerating and decelerating between an upper and. lower speed 

 limit and while such a system could theoretically be employed if the 

 flywheel were made large enough, it was obviously preferable to 

 employ a type of regulator in which the speed was inherently held 

 constant without such acceleration and deceleration. 



The regulating circuit employed is shown in Fig. 10. The complete 

 theory of this regulating circuit is to be covered in another paper to 

 be presented before the Institute. Briefly, the principle consists in 



