796 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



Table III — Relative Performance of Alternative 

 Television Waveforms 



* The waveforms are numbered to correspond to those given on Fig. 9. 



t All values referred to E.C.R. = 3^^; plus values indicate poorer performance. 



X All values referred to E.C.R. = 3^^; Group 1 products are those whose mag- 

 nitudes are directly proportional to the carrier magnitude. Group 2 products 

 are those whose magnitudes are proportional to the S(5[uare of the carrier 

 magnitude. 



One of the important factors in setting repeater spacing is the mag- 

 nitudes at which signals are transmitted in the system and the relation 

 between these magnitudes and signal-to-noise and repeater overload 

 performance. In the all telephone system (1,860 channels), the telephone 

 levels (db with respect to the transmitting toll test board) were set to 

 optimize signal-to-noise performance. To avoid penahzing the channels 

 in the upper part of the band where random noise tends to be much 

 higher than at low frequencies, the levels of the three mastergroups are 

 staggered. At the output of any repeater in the high frequency line, the 

 nominal level of mastergroup No. 1 is —21 db, that of mastergroup 



16 



12 



I 2 3 4 5 6 8 10 ^ 20 30 40 60 80100 20( 



PICTURE TUBE BRIGHTNESs''B"iN FOOT LAMBERTS 



Fig. 10— Picture tube interference sensitivity assumed for L3. 



