506 



BELL SYSTEM TECHNICAL JOURNAL 



. . . ". Native English callers were used at the transmitting end of 

 the circuit almost exclusively and experienced articulation observers 

 were used at the receiving end. Figures 12 and 13 show the articu- 



70 



50 



uj 40 



30 



i= 20 



10 



5 10 15 20 25 30 35 40 45 



DOUBLE SIDEBAND SIGNAL-TO-NOISE RATIO IN DECIBELS 



50 



Fig. 13 — Plot of per cent articulation errors on double-sideband vs. double-sideband 



signal-to-noise ratios. 



lation errors observed on the single and double-sideband transmissions 

 plotted against the signal-to-noise ratios measured on the double- 

 sideband receiver. When plotting the single-sideband data, the 

 average of two successive signal-to-noise ratio readings on double- 

 sideband was taken as the signal-to-noise rafio for plotting the inter- 

 vening single-sideband observation. The improvement due to the 

 use of the single-sideband system expressed in decibels is the difference 

 in the abscissa* of the two curves for a given ordinate. The second 

 curve of Fig. 12 has been dotted in on Fig. 13 to facilitate the com- 

 parison of the two systems. The improvement is seen to average 

 about 8 db for intermediate values of signal-to-noise ratio. 



Figures 14 and 15 show the circuit merits obtained on the single 

 and double-sideband systems respectively plotted against the field 

 strength measured on the double-sideband receiver. A circuit having 

 a merit of 5 is an extremely good circuit, while a circuit having a merit 



