SYNCHRONIZATION OF TELEVISION 



609 



by the fact that if it were rapidly turned it would throw the motor 

 out of step. 



As an aid to framing, therefore, a second two-pole low frequency 

 interlock was added to the system by providing the d-c. motors on 

 each end with a pair of slip rings tapped to two opposite commutator 

 bars. The d-c. shunt motors thus acted as converters furnishing 

 17.7 cycles at 1062.5 r.p.m. With this added feature on both the 

 transmitting and receiving motors the process of synchronization was 



OVOLT O.C. .POWER 



VOLT C POWER 



Fig. 4 — Complete circuit of synchronizing system 



first to close the 17.7-cycle circuit and adjust the field rheostat of the 

 receiving motor until it came into step. Since this was a two-pole 

 circuit there was only one angular position at which synchronization 

 could occur. The high frequency synchronous machines were then 

 connected together, thereby limiting the phase displacement to within 

 .07 degree, as previously described. The high frequency motors in 

 this system take the variation in load while the low frequency motor 

 takes care of the steady constant component of load. Incidentally 

 the addition of the low frequency synchronous motors greatly facili- 

 tated the synchronization of the high frequency motors inasmuch as 

 it insured the proper initial speed. When the high frequency switch 

 was closed there was merely a slight shift in phase angle to bring the 

 receiving motor into step. The schematic circuit of the system thus 

 far described is shown in Fig. 3. 



