Sri'DlIiS IX RADIO BROADCAST TRAXSMISSION 



203 



the changes in length of one vector will lag the changes in length of 

 the other by an amount 



4>=v(^t) (16) 



when A/ equals the difference in time of transmission over the two 

 paths and v is the angular velocity of the modulating tone. This 

 angle </> for 500-cycle modulation may according to the data thus 

 far described, amoimt to more than 00 degrees at the receiving points 

 selected for obser\ation. 



In addition to the lag in amplitude there will be a lag in frequency 

 change over the frequency modulation cycle. This lag which has 



Fig. 46 — Graphical method of synthesizing distorted wave forms caused by frequency 



modulation 



already been shown in connection with the analysis of distortion in 

 certain types of band fading records (see Fig. 22), becomes a change 

 in the relative phase angle of the vectors under consideration. Thus 

 our picture finally becomes one of two vectors changing in length, 

 the changes In one continually lagging the changes in the other, the 

 tw^o vectors at the same time undergoing what we might term a 

 relative angular wobble. 



In Fig. 46 these relations are produced graphically. For our pur- 

 poses we might assume that the vector representing one field is fixed 

 and allow the other one to wobble the relative amount. At an 



