AUTOMATIC PRINTING EQUIPMENT 409 



simplex operation of cables. The character of the received signals and 

 interference on long cables is such as to require the use of entirely 

 different methods of reception in order to utilize the line time most 

 efficiently, and the higher transmission speeds expected on cables 

 necessitated departure from standard land line practices in the matter 

 of apparatus design and number of channels employed. The system 

 as finally developed embodies the following important improvements 

 over previous methods. 



1. An entirely automatic means for quickly reversing the direction 

 of transmission on a simplex circuit at short intervals which can be 

 altered as required to accommodate varying traffic loads in the two 

 directions. 



2. A synchronous vibrating relay which corrects for the residual 

 distortion in the signals delivered by the amplifier, and practically 

 doubles the speed of transmission. 



3. A high degree of precision and refinement in the design and 

 construction of apparatus which is justified by the great cost of the 

 cable relative to that of the terminal apparatus. 



The inclusion of these improvements in a modified multiplex system 

 involved, of course, the solution of a number of important incidental 

 problems such as the provision of Morse "talking circuits" which could 

 be made instantly operative, and the development of suitable arrange- 

 ments for linking two simplex cable sections together through re- 

 peaters. 



Two Directional Working 



The use of duplex methods in the operation of non-loaded cables 

 enables communication to be carried on simultaneously in both 

 directions and usually effects an increase of from 60 to 90 per cent in 

 the total traffic capacity of the cable. As only a moderate capita! 

 expenditure is required to equip a non-loaded cable for duplex operation 

 practically all cables of this type are now equipped in this way as a 

 matter of economy. The characteristics of the loaded cable, however, 

 are such as to require the use of highly complicated and extremely 

 expensive artificial lines and balancing equipment for duplex operation 

 and it is quite doubtful whether the total duplex traffic capacity thus 

 secured would equal that obtainable by the use of simplex methods. 

 Duplexing the loaded cable therefore appeared to afford no certain 

 economic gain over simplex operation and the extremely high cost of 

 duplexing could hardly have been justified merely for the sake of 

 securing simultaneous transmission in both directions. 



The apparatus and methods formerly employed for reversing the 



