48 



BELL SYSTEM TECHNICAL JOURNAL 



the United States. One of these, designed for the longer hauls, pro- 

 vides on one pair of wires three telephone circuits in addition to the 

 voice frequency circuits. These three carrier circuits are provided 

 by the modulation of frequencies between about 6,000 and 28,000 



CHANNEL 



I 

 NUMBER 



CHANNEL 



I 

 NUMBER 



FIRST SYSTEM 



2 EAST I EAST 3 EAST 



SECOND SYSTEM 



^ 



a EAST 1 EAST 



3 EAST 



8 



la 



16 



ao 



24 



28 



32 



FREQUENCY- KILOCYCLES PER 



SECOND 



Fig. 39 — -Frequency allocation of two long haul carrier systems. The blocks 

 indicate the range of the transmitted side band. The arrows are located at the carrier 

 frequencies and indicate the direction of transmission. 



UJ 



>■ UJ 

 O -I 



m 

 o — 

 o o 

 o^ 



5e^ 

 O z 



a: u 



1^ _] 



z$ 



9.3 



< u 



> 



UJ 

 Q 



M 



12 



10 



2 - 



-2 





400 800 laOO 1600 2000 



CYCLES PER SECOND 



2400 



2800 



3200 



Fig. 40 — Average overall transmission-frequency characteristic of Long Haul Carrier 



telephone system. 



cycles, different frequencies being used for transmission in the two 

 directions. The different conversations are amplified together in a 

 common repeater at intermediate points and at the terminals sep- 

 arated by electrical filters providing for each circuit a band of approxi- 

 mately 3,000 cycles. The frequency allocation for two varieties of 



