STUDIES IN RADIO BROADCAST TRANSMISSION 



175 



transfer from transmitter to receiver takes place over two paths of 

 different lengths one wave will constantly lag behind the other. 



This lag may be measured as a time interval. In Fig. 23 are shown 

 two waves, (a) and (b) of constant amplitude but with frequency 



Sinusoidal Frequency Variation 



Stepped Frequency Variation 

 _fUndisfcorhed Interval 



Fi^r 22-Curves showing the relative effect of transmission time lag in sinusoidal and 

 Fig. 22 '-"'^^^^""°^p.|,y.step methods of frequency variations 



Fig. 23— Diagram showing the effect of frequency modulation 



modulation. The wave (b) representing the indirect wave it will 

 be noticed, lags behind the direct wave represented by (a). Ihe 

 amount of this lag is determined by the difference in length of path 

 and the transmission velocity. If we were to receive only one wave, 

 as we should in the daytime, for example, we would hnd it to be a 



