STUDIES IN R.iniO BROADCAST TRANSMISSION 



205 



For purposes of comparison, a set of oscillograph pictures of rep- 

 resentative received wave shapes is shown in Fig. 48. These repre- 

 sent the actual effect of night-time transmission with frequency 

 modulation between 463 West Street, New York City and Stamford, 

 Conn.; the modulating tone was a practically pure 264-cycle sinu- 

 soidal wave. The samples have' been arranged in successive order 



Fig. 48 — Oscillograms showing actual wave forms with distortion resulting from fre- 

 quency modulation 



to correspond with the order shown in Fig. 47. There exists a striking 

 similarity. Occasionally, however, the shapes predicted may depart 

 considerably from those obtained experimentally. As an example of 

 such a departure, the record (h) in Fig. 48 has been included. Such 

 unusual samples may be due to a combination of waves arriving over 

 more than two paths or it may be that the time variation of the 

 frequency is far from the simple sinusoid which we have assumed. 

 As a matter of fact, a critical mathematical treatment of this case 

 shows that only an approximation of such a sinusoidal condition is 



