A CARRIER TELEPHONE SYSTEM FOR TOLL CABLES 



85 



single sideband method of transmission is employed, with carrier fre- 

 quencies suppressed. The choice of a group comprising 12 channels 

 was influenced not alone by the requirements of the type K system 

 itself but also by those of other broad-band systems. From the 

 earliest stages of the broad-band development it was recognized that 

 there would be considerable advantage from the standpoints of flexi- 

 bility of interconnection, of minimum development effort, and of large 

 scale production of equipment units, if the designs of different broad- 

 band systems could be so coordinated as to enable the same design 

 of channel terminal equipment to be employed for each. A common 

 12-channel terminal unit developed for this purpose is used in the type 

 K system. 



15.0 



m 10.0 

 o 



(O 5.0 



o 



_l 



^ 2.5 



tr 

 -2.5 



-5.0 



500 1000 1500 2000 2500 3000 

 FREQUENCY IN CYCLES PER SECOND 



Fig. 3 — Transmission frequency characteristics of overall circuit. 



The spacing of the channels in broad-band systems is important 

 from the standpoint of the channel selecting circuits and the width of 

 the derived voice circuit. As discussed in a recent article, a uniform 

 4000-cycle interval has been adopted for the different channels of all 

 broad-band systems.^ The speech band width obtained with this 

 spacing is in keeping with recent improvements in telephone instru- 

 ments and other parts of the telephone plant. Overall transmission- 

 frequency characteristics for a single link and a five-link connection 

 are shown in Fig. 3. 



Cable Attenuation 



The type K system is designed to be applied to the No. 19 AWG 

 (0.9 mm.) pairs commonly found in existing cables. (The Morristown 



