TRANSMISSION SYSTEM FOR TELETYPEWRITER 



545 



Another method for connecting to subscriber stations which cannot 

 be cared for by a metallic cable pair employs a simple telej^raph re- 

 peater installed as part of the subscriber station equipment. This 

 arrangement as well as the one previously described has the advantage 

 that it permits polar signals to be used in both directions over the sub- 

 scriber line. 



In a few cases which have arisen where telegraph facilities were not 

 readily available between the teletypewriter center and a subscriber 

 station, use has been made of a single-channel voice-frequency carrier 



MARK *i* — SPACE >-«— MARK ■»!«— SPACE — ^ 



f ^ [ ^ r - 



-MARK >r^SPACE * 



^ 



-SPACE-^ 



Z 



Fig. 7 — Effect of wave shaping networks in long subscriber lines operated over 



cable pairs. 



A — Current at subscriber station; no wave shaping network used. 



B — Current in A as received at central ofifice. 



C — Current at subscriber station; loop equipped with wave shaping network. 



D- — Current received at central office; loop equipped with wave shaping network. 



R — Current required to operate receiving relay of repeater in central ofifice. 



telegraph arrangement by means of which the transmission takes 

 place over standard telephone circuits. A small carrier telegraph 

 terminal arrangement is mounted on the back of the teletypewriter 

 table, and a corresponding carrier terminal is located in the tele- 

 typewriter center in a trunk circuit between the teletypewriter 

 switchboard and the telephone toll board. Special operating pro- 

 cedures are set up so that whenever the subscriber initiates a call, 

 connection is established by telephone operators t)ver telephone 

 circuits to the above mentioned carrier trunk circuit at the teletype- 

 writer center, and the teletypewriter switchboard operator is notified 



