A SINGLE-SIDEBAND SHORT-WAVE SYSTEM 



505 



Upon occasions, advantages considerably higher than the average 

 were obtained for the single-sideband system. Reeves ^ has shown 

 that at times the two sidebands of a double-sideband radio system are 

 likely to be shifted in phase relative to each other and the carrier in 

 such a manner that the demodulated audio-frequency components 

 add at random rather than directly in phase. Under such circum- 

 stances the received signal-to-noise ratio of the transmissions would 

 be reduced by 3 db, and in comparison with the single-sideband 

 system the latter would show a correspondingly greater improvement. 

 Further, under bad fading conditions, some advantage might be 

 expected from using a receiver in which provision is made to insure 

 an adequate carrier in the second detector at all times. The single- 

 sideband receiver used in these tests had such provision while the 

 double-sideband receiver did not. 



70 



O 50 



? 30 



5 10 15 20 25 30 35 40 45 50 



DOUBLE SIDEBAND SlGNAL-TO-NOlSE RATIO IN DECIBELS 



Fig. 12 — Plot of per cent articulation errors on single-sideband vs. double-sideband 



signal-to-noise ratios. 



The articulation of the two systems was compared by using words, 

 which averaged approximately three syllables, taken at random from 

 the dictionary. They were inserted in the phrase "Write down 



^ Journal of the Institution of Electrical Engineers, September, 1933, page 245. 



