418 BELL SYSTEM TECHNICAL JOURNAL 



impose quite severe requirements upon the mechanical as well as the 

 electrical portions of the apparatus. In designing the apparatus, the 

 greatest care was therefore exercised in selecting, for the construction 

 of even the smallest details, materials which would withstand the 

 most severe usage and be unaffected by the most severe climatic 

 conditions. 



Summary of System 



The inclusion of these newly developed features in the multiplex 

 system and the application of the modified system to a long loaded 

 cable presents a number of interesting aspects and new possibilities. 

 The entire system is shown schematically in Fig. 7. 



The use of an amplifier containing no mechanical moving parts, 

 in which all adjustments are made by alteration of the constants of 

 electrical circuits, makes it possible to determine at the time of 

 installation the proper amplifier adjustments to give satisfactory 

 signal shape at a number of different transmission speeds and thereafter 

 the amplifier may be quickly set for any speed by duplicating the 

 adjustments that were previously found suitable for that speed. As 

 the operation of the correcting relays and circuits and the vibrating 

 relay depends to some extent upon the shape of the signals delivered 

 by the amplifier, the ability to reproduce accurately a signal shape 

 which has been previously found satisfactory is of considerable 

 importance in the operation of the system. 



Although the amplifier and shaping networks are considered a part 

 of the cable system rather than an element in the transmitting and 

 receiving system, their operation must be controlled by the direction 

 control switching mechanisms. The relays included in the direction 

 control system which switch the amplifier circuits are built in the 

 amplifier to simplify wiring and maintenance. The speed of the 

 distributors is controlled as in the multiplex system by vibrating 

 tuning forks, but in order to secure under certain conditions greater 

 stability and freedom from speed variations due to alteration in the 

 fork contact adjustment and changes in room temperature and voltage 

 of the power supply there was developed a constant temperature 

 vacuum tube driven fork. The distributor, with its driving fork, the 

 relays included in the direction control and vibrating relay circuits, 

 and the apparatus usually provided in land line multiplex equipments 

 for phasing and lining up the circuit, including the Morse talking 

 circuit, are mounted in accessible positions on a table which is separated 

 from the operating tables on which the printers and transmitters are 

 located. 



