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BELL SYSTEM TECHNICAL JOURNAL 



carrier channels. The general arrangement of this equipment in the 

 circuit is shown in further detail in Figure 27. This includes the 

 signaling equipment and makes provision for the connection of a 

 balancing network. 



The use of a two-wire termination for the carrier system is necessary 

 because ordinary telephone circuits at the switchboards, such as 

 trunks, subscribers' lines, etc., are of the two-wire type and the cord 

 circuits for interconnecting these are of this type. Hence, such a 

 termination of the carrier system makes it possible to connect it to 

 other circuits with the same apparatus and in the same manner as 

 with ordinary telephone circuits. 



The signaling apparatus consists of a 1,000-cycle ringer of the type 

 which is employed on long voice-frequency lines. This is connected 

 to the voice-frequency terminal of the carrier system in the same 

 manner as to other voice circuits. The use of 1,000-cycle signaling 

 with the carrier has been desirable in place of the more simple low- 

 frequency signaling apparatus used on shorter lines, since frequencies 

 less than 200 cycles are not efificiently transmitted. 



SWITCHBOARD 



Figure 28 — Schematic of 1,000-cycle ringing circuit 



Figure 28 shows a simplified diagram of this type of ringer. The 

 transmitted signaling currents as impressed upon the carrier channel 

 are of 1,000-cycle frequency interrupted at a speed of 20 interruptions 

 per second. This ringing current supply is obtained either from 

 1,000-cycle generators or vacuum tube oscillators. Such currents, 

 while in the voice-frequency range and thus capable of being trans- 

 mitted readily, form a signal of sufficiently distinctive character to 

 permit separation from ordinary voice currents. Thus, practical 



