38 



BKLL SYSTEM TECUM CAL JOURNAL 



and the nuniljcr (jf c\cles per second for each ciiannel = (1/c) 

 •(l/2)(a/6j^«2 ^'^ 



The angular opening of the frame a = 36()/w X C. 

 Tlie number of picture elements = n~'{alb). 



These formuke ma>' he utilized upon assuming values for any of the 

 variables, to fix the values of the other. In the present case, it was 

 decided for reasons of simplicity to restrict the number of channels to 3. 





L2L1 



l-c 





1-b 



Fig. 1 — Schematic of three-channel television apparatus, {a) Receiving end 

 disc with spiral of holes provided with prisms. (6) Sending end disc with circle of 

 holes provided with prisms, (c) General arrangement of apparatus. 



The band width was chosen as that found feasible in the two-way 

 tele\'ision system, namely 40,000 cycles. The picture shape chosen 

 was that of the sound motion picture, for which ajb = 1 j6. The 

 repetition frequency assumed was 18 per second, again following 

 closely that of existing experimental synchronizing apparatus. Sub- 

 stituting these w'llues in the formula rearranged to give ;/, we get for 

 the nimiber of holes, 



and for a, 



ilBbc 



F 



^a 



= 108 



— X 3 = 10 degrees, 



for the number of picture elements. 



n = (108)2 X ^ = 13,608. 



In utilizing the prism disc principle at the sending end, direct 



