524 



BELL SYSTEM TECHNICAL JOURNAL 



75 



70 



65 



) 



160 



) 

 J 

 155 



Jso 



•45 



J 



Uo 

 ) 



)35 



[ 30 

 J 

 ) 25 



) 



i 20 

 ) 

 [ 

 15 



10 



5 



10 20 40 60 80 100 200 400 600 1000 2000 4000 10,000 



RADIO SIGNAL BANDWIDTH IN MEGACYCLES PER SECOND 



Fig 17 — PCM FM; performance with respect to C\V and similar system interference 

 for lUOO 4-kc channels. Relations between h:inclwidth and aiuMo sig lal-to-noise ratio 

 showing optimum bases for different ratios of FAI wave to interference. 



and the minimum band width becomes 



5 = ,8 + 2 ^6 = 2hF^ 



For Q/P = 0.3535 (9 db) the minimum required value of ^ is halved so 

 that 



For QIP = 0.118 (18.5 db) the minimum required value of /3 is further 

 reduced threefold so that 



The curves of Fig. 17 are calculated from these relations. 



With interference from a similar system a number of necessary conditions 

 must be met. If the systems are similar in PCM base and in radio fre- 

 quency, the sustained beat frequencies that may occur are /3/(6 — 1) and 



