A SINGLE-SIDEBAND SHORT-WAVE SYSTEM 



507 



of 3 is only just commercial and one having a circuit merit of 2 is 

 useful only as an order wire. It will be noted that the difference 

 between the curves for a circuit merit of 3 is about 8 db, for a circuit 



< 



i/av 



30 



40 



FIELD STRENGTH IN DECIBELS ABOVE -j:^ 

 Fig. 14 — Plot of circuit merit vs. field strength on single sideband. 



merit of 4 about 5.5 db, and for a circuit merit of 5 about 4.5 db. This 

 is in fair agreement with the signal-to-noise and articulation data. 



The comparison of two circuits in this manner is undoubtedly of 

 value if the observations extend over a period of time and if the 

 individual observations are separated by a sufficient interval. When 

 the observations are spaced at short intervals, however, the observer 

 is bound to be influenced by the previous observation and it seems 

 likely that the resulting comparison may be considerably in error. 

 For instance, the observer may notice a small diflference in circuit 

 merit and consequently consistently rate one circuit a half point higher 

 than the other, when the actual difference might be nearer to ^ of a 

 point. For this reason it is believed that the comparison of the two 

 systems by means of circuit merit gives a less accurate result than by 

 either signal-to-noise or articulation tests. 



