10 



BELL SYSTEM TECHNICAL JOURNAL 



In estimating the interference the carrier beat can be considered by 

 itself and from the data at hand there can be derived the areas around 

 each of two stations having approximately the same carrier frequency, 

 inside of which the amplitude of the beat note will be down a given 

 number of db from that of the desired speech. The same is true of the 

 interfering speech when it is different from the desired speech. The 



1.0 



.0011 

 .0001 



%- 



.001 .01 



RATIO OF CARRIER AMPLITUDES 



Fig. 3 — -Relative amplitudes of undesired frequencies as a function of the ratio 

 of the amplitudes of the desired and the interfering carriers. Modulation of desired 

 station large and of interfering station small. 



frequencies {p i zO'^Tr, (g ± iC)11-k. (p±qdz u)'2ir, etc., will coml>ine 

 to form a disturbing background which we shall designate as "displaced 

 side band interference." This may be taken to include all of the 

 interfering frequencies except those of the undesired speech and its 

 entirely unimportant harmonics. (The frequency 2p'2ir is not here 

 classed as an interfering frequenc}'.) 



