Synchronization System for Two-Way Television * 



By H. M. STOLLER 



In a previous paper presented before the June, 1927 Convention of the 

 American Institute of Electrical Engineers, the method of securing syn- 

 chronization of television signals was described as employed in the Bell 

 System Television demonstration of April, 1927. The present paper de- 

 scribes the development of a new control circuit which is in use in the new 

 two-way television system between the Bell Telephone Laboratories at 463 

 West Street and the American Telephone and Telegraph Company build- 

 ing at 195 Broadway, New York. 



TELEVISION transmission requires not only synchronization of the 

 transmitting and receiving equipment but such synchronization 

 must be held to a narrow phase angle so that the scanning discs at the 

 transmitting and receiving end will never depart more than a small frac- 

 tion of a picture frame width from the desired position.^ In the 1927 

 demonstration, 2125 cycle synchronous motors were employed with 

 supplementary D.C. motors to facilitate starting. This plan required 

 the use of vacuum tube amplifiers of large size in order to supply suf- 

 ficient power to the synchronous motors. 



Such high frequency synchronous motors, however, are inefficient 

 and expensive, so that when designing the new system, it was desired 

 to solve the problem of synchronization with simpler and cheaper 

 equipment and in a manner which would require less attention in 

 starting. It was particularly desired to employ a motor which could 

 be operated directly from the 110 volt lighting circuit without any 

 auxiliary "A", "B" or "C" batteries for the control equipment. 



Description of Motor 



Figure 1 shows a photograph of the new television motor and its 

 associated control equipment. 



The motor is a four pole compound wound D.C. motor with the 

 following special features added. 



1. An auxiliary regulating field, the current through which is controlled 



by the vacuum tube regulator. 



2. A damping winding on the face of the field poles to prevent the field 



fiux from shifting (Fig. 3). 



* Presented at June, 1930, meeting of A.I.E.E., Toronto, Canada. 

 1 These requirements are more fully discussed in a previous paper. {Journal of 

 the A. I. E. E., Vol. 46, page 940, 1927.) 



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