610 



BELL SYSTEM TECHNICAL JOURNAL 



Synchronization Over Long Lines 



The above description explains the action of the synchronization 

 system over Hnes of neghgible impedance. In order, however, to 

 secure similar results over a long distance telephone line or radio 

 channel it is necessary to first attenuate the high and low frequencies 

 to a power which can be safely applied to the transmitting end of 

 the line and then amplify the power at the receiving end to restore it 

 to the proper level. Fig. 4 shows the complete system employed. 



Fig. 5 — Large scanning disc motor 



While the high and low frequency machines on the transmitting 

 end could have been designed so as to produce exactly the right power 

 level, it was desirable, for the sake of interchangeability, to build the 

 transmitting and receiving motor equipment of the same size. The 

 output from the transmitting high frequency generator (shown in 

 Fig. 2) when untuned was approximately 17 volts at 2125 cycles. 



