692 



THE BELL SYSTEMj[tECHNICAL JOURNAL, JULY 1952 



100 

 90 

 80 

 70 

 60 

 50 

 40 



80 100 120 140 



OPEN-WIRE LENGTH IN MILES 



Fig. 2 — Distribution of circuit lengths in Iowa in 1950. 



5< 



'iV, 70 



°a: 30 



12 



13 



1 23456789 10 11 



NUMBER OF CIRCUITS PER GROUP 



Fig. 3— Distribution of circuits per group in Iowa in 1950. 



OA 



-OB- 



4_ -H^^H-^H^^ 



LOW HIGH LOW HIGH LOW HIGH LOW HIGH 



24 32 40 50 60 70 80 90 100 110 120 130 140 150 160 

 FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 4 — carrier telephone — frequency allocation. 



