CABLE CARRIER TELEPHONE TERMINALS 123 



panel. The bays of this type are located near their associated channel 

 equipment because the supply is chiefly for channel modems. One 

 carrier distributing unit provides for the even and another for the odd 

 harmonics. All terminals and bus bars of these units which are com- 

 mon to the ten systems are protected by insulating covers. 



The four-wire voice-frequency jacks for all the systems in an office 

 will ordinarily be grouped in associated bays, one of which is shown on 

 Fig. 9, A. A bay will accommodate five systems as an average, that 

 is, 60 voice circuits including the necessary pads and telephone set. 



The high-frequency testboard is an arrangement of sealed test 

 terminals, high-frequency patching jacks and high-frequency testing 

 equipment mounted on bays as shown in Fig. 9, B. Only a few high- 

 frequency patching jacks were required initially and these were there- 

 fore mounted above the sealed terminals. This arrangement of bays 

 with the addition of a high-frequency patching bay at the right of 

 each sealed terminal bay will accommodate 100 systems. 



The carrier pairs are split off from the main toll cables at splices in 

 the cable vault. The input circuits are carried thence in lead covered 

 cable to the cable crosstalk balancing bays and thence to the input 

 sealed terminal. The output pairs run directly from the output 

 sealed test terminal to the splice in the cable vault. The remaining 

 high-frequency wiring from rack to rack is shielded wire. 



Conclusion 



The carrier telephone terminals for the type "K" system which have 

 been described are simpler, occupy less space and provide better trans- 

 mission performance than multi-channel carrier terminals used pre- 

 viously in the Bell System. As part of a general development of 

 broad-band transmission systems, it is very desirable to employ equip- 

 ment which can be used in common with several systems. The 12- 

 channel bay, much of the carrier supply and all of the voice-frequency 

 terminating equipment of this type "K" system terminal will be used 

 to form corresponding parts of the terminals for the 12-channel open- 

 wire system and the coaxial system, both of which are under develop- 

 ment. This not only has simplified the development work, but also 

 will result in greater mass production of these common parts and pro- 

 vide desired uniformity of voice-frequency terminating levels and 

 maintenance arrangements. 



References 



1. "Carrier Current Communication on Submarine Cables," H. W. Hitchcock, Jour, 

 of A. I. E. E., October 1926; Bell Sys. Tech. Jour., October 1926. 



