COMMON FREQUENCY BROADCASTING 



599 



tempt to present any graphical summation of the effective distortion 

 present in the reception of an ordinary broadcast program under such 

 conditions. On the other hand these theoretical studies were un- 

 dertaken in order to explain certain phenomena observed during the 

 preliminary field tests as the degree of modulation and the field strength 

 ratio were varied. The actual results have been quite closely corrob- 

 orated by the conclusions reached from a study of these single fre- 

 quency curves which have been of great value in obtaining a physical 

 picture of the conditions that exist in this middle area. 



U -I 



Q in 



Q. UJ 



OZ 



loz -20 



u. < 



OQ 



30 



r 



60 90 120 150 



RADIO PHASE ANGLE IN DEGREES 



Fig. 17 — Same as in Fig. 15 except that £1/^2 = 0.5. 



These curves have been limited, for the sake of simplicity, to the 

 consideration of the conditions at the points in the middle area equi- 

 distant from the two stations. It will be seen from these curves for this 

 limited case that if, with equal degrees of modulation, each individual 

 frequency component of the program could be synchronized at the 

 two transmitters no additional distortion would be caused at these 

 points by the isochronous operation of the two stations. But for 

 points not equidistant the audio phase angle will not be zero even 

 though it is maintained so at the transmitter and the magnitude of 

 this divergence from synchronism will be different for each audio 

 frequency and for each separate point in space. The magnitude of 

 this divergence increases rapidly as the distance to the respective 

 stations becomes more unequal. Furthermore, the problem of main- 

 taining in synchronism every component of the broad frequency spec- 

 trum required for program transmission appears to offer tremendous 

 technical difficulties. 



