SHOKT-IIAUL CARRIER TELEGRAPH 687 



carried throusli a cut-off jack. Tho toll operators then can patch the 

 circuit to the subscriber, thus by-j)assiiig the main line when it is in 

 trouble. Since the telegraph eiieigy from only one channel is impicssed 

 on tlie emergency circuit, no adjustment of levels is required. 



The channel terminals which are at the central office, shown at the 

 left of Figs. 12 to 16, may be connected to subscribers over do loops or 

 they may be connected to other types of telegraph repeaters. Fig. 17 

 indicates the latter connection schematically. Since the loop circuit must 

 supply positive potential to the 43A1 channel terminal, the connecting 

 repeater must be arranged to supply positive battery for marking signals. 



FUTURE EXTENSIONS 



It is expected that the field of application of the 43 A 1 system will be 

 broadened by further development over the next few years. More fre- 

 quencies will be pro\'ided, ])oth in and al)ove the voice band. Means will 

 be designed for passmg TWX super\isory signals over a direct-current 

 loop from a subscriber station to a channel terminal installed in a nearby 

 central ofhce. The built-in supervisory arrangements of the 43 A 1 ec^uip- 

 ment will be exploited to obtain inexpensive straightforward trunks 

 for use both between TWX switchboards and from switchboards to 

 Line Concentrating Units. The supervisory feature will also be employed 

 in pri\-ate line ser\dce to provide an open circuit alarm. 



REFERENCES 



1. R S. Caruthers, H, R. Huntley, W. E. Kahl, L. Pedersen, "A New Telephone 



Carrier System for Medium-Haul Circuits," Elec. Eng., 70, pp. 692-697, Aug. 

 1951. 



2. B. P. Hamilton, "Carrier Telegraphy in the Bell System," Bell Labs. Record, 



26, pp. 58-62, Feb. 1948. 



3. J. A. Duncan, R. D. Parker and R. E. Pierce, "Telegraphy in the Bell System," 



A.I.E.E. Transactions, 63, pp. 1032-1044, 1944. 



4. B. Ostendorf, Jr., "New Electronic Telegraph Regenerative Repeater," Elec. 



Eng., 69, pp. 237-240, March, 1950. 



5. R. L. Case, "Transmission Features of V3 Repeaters," Bell Labs. Record, 27, 



pp. 94-95, March, 1949. 



