COAXIAL CABLE SYSTEM FOR TELEVISION TRANSMISSION 455 



relative time relationship as they are generated. Referring back to 

 Fig. 8, it was assumed that no picture element could be displaced by 

 more than about half its width. This led to the decision to hold 

 frequencies between 806,000 and 3000 cycles to a delay distortion of 

 about 0.3 microsecond. For a similar degradation of detail in the 

 vertical direction, the permissible delay distortion is 280 times as 

 great which, in a system of this type, is very easily obtained. The 

 actual circuit roughly met these requirements as indicated by Fig. 15, 



-1 



-570 



to 



Q -565 



z 



o 



o 



u 



</1 -560 



O 



a. 

 o 



2 -555 



z 



5 -550 

 _l 



UJ 



o 

 -545 



< 



£-540 



-535 



-530 



-525 



60 



100 200 500 1000 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 15 — Phase delay of New York-Philadelphia television circuit. 



which shows the phase delay characteristics of the line, repeaters and 

 equalizers, and of the overall circuit at the frequencies used for trans- 

 mission. 



Noise or interference is very annoying in television transmission; 

 and pattern, or single frequency interference, is particularly objection- 

 able. The permissible noise or interference depends on the amplitude 

 range of the reproduced picture. During these experiments, it was 

 found that a substantially linear response could be obtained over a 

 signal current range of about 20 db — a brightness ratio of 10 to 1. 



