THE L3 SYSTEM — DESIGN 



793 



modulation of a carrier with one sideband partially suppressed, i.e., 

 vestigial sideband transmission. There remained, however, three major 

 problems for detailed study; (1) the transmission of dc components of 

 the video signal; (2) the per cent modulation of the carrier which for 

 convenience is defined in terms of ''excess carrier ratio", the ratio of the 

 peak (white) signal to the peak-to-peak composite signal as measured in 

 the carrier frequency envelope; and (3) the sign or sense of modulation, 

 that is, whether increasing or decreasing brightness should correspond 

 to increasing signal voltage on the high frequency Hne. Typical wave 

 forms illustrating the alternatives are shown in Fig. 9. 



^___R___^ 



.IS. 



(a) 



VIDEO WAVEFORM 



IT. 



4d 



Jl 



_J-L 



¥ 



(b) 



NO DC COMPONENTS 

 100%^TOSITIVE" 

 MODULATION FOR 

 WHITE BLANK FIELD 





JT 



Jl- 



ir 



-i_r 



Jl 



u 



(c) 



DC COMPONENTS 

 TRANSMITTED 

 100%''NEGATIVE" 

 MODULATION 



(d) 

 DC COMPONENTS 

 TRANSMITTED 

 509^ "POSITIVE" 

 MODULATION 

 (E CR = 2) 



X---^ 



(e) 



DC COMPONENTS 

 TRANSMITTED 

 100»/o" POSITIVE" 

 MODULATION 

 CECR=0 



J^ 



^ 



Ul Jl 



hi inrir 



11 



(f) 



DC COMPONENTS 

 TRANSMITTED 

 GREATER THAN 

 100% MODULATION 

 (ECR=1/2) 



Fig. 9 — Typical television signals. Alternative carrier frequency waveforms. 



