including points where cable and open wire are joined, other than the 

 standard telephone repeaters and associated apparatus already pro- 

 vided with the circuit for telephone purposes. 



Still a third type of telegraph system devised to meet the new condi- 

 tions is that known as the high-frequency carrier telegraph system. 

 This system is designed for application to open wires. It applies to 

 the provision of telegraph circuits the same principles as are applied 

 in the carrier telephone system for the provision of telephone circuits. 

 It uses frequencies above the voice range, roughly in the range from 

 3,000 to 10,000 cycles, thus permitting the continued use of the 

 conductors for a voice-frequency telephone circuit simultaneously 

 with its use for high-frequency carrier telegraph circuits. With this 

 system 10 two-way telegraph circuits are provided. 



Auxiliary Apparatus and Equipment 



In addition to the main items described above, developments of 

 other apparatus and equipment auxiliary to the telephone toll circuits 

 were made necessary by the general use of repeaters and carrier 

 systems. Power plants providing current to the filaments and plate 

 circuits of the vacuum tubes used in repeaters and carrier systems had 

 to be provided having much closer voltage regulation than had hereto- 

 fore been necessary for the earlier types of telephone equipment. New- 

 forms of testboards were required and new types of arrangements of 

 distributing frames and of protective apparatus. Plans were devel- 

 oped for the economical arrangement of the new types of equipment 

 in large offices. All of these things while essential for the proper 

 operation of modern toll telephone circuits probably do not need de- 

 tailed discussion in this statement. 



Another type of equipment which had to be developed was that for 

 carrying out the various forms of electrical test necessary to assure 

 the proper operation of these new' telephone circuits. The develop- 

 ment of this equipment and of the new maintenance methods which 

 made use of this equipment is of sufficient general importance so that 

 it is briefly discussed in the next section of this statement. 



Development Of Methods Of Measurement And 

 Maintenance For Toll Circuits 



The history of toll service has been a story of the continuous appli- 

 cation of new scientific instrumentalities. The laboratory experi- 

 ments of one day become the regular service-giving apparatus of ever- 

 growing complexity. Maintaining this complicated equipment at a 

 high state of efficiency has been accomplished through methods of 



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