Types of Carrier Telephone Systems

Figure 18. Approximate frequency allocations of certain carrier telephone systems used in the United States. The improved type C5 carrier uses the CS and CN allocations. The type E is a power-line carrier system. Two systems not shown are the type L (page 432),used on coaxial cables, and the type M (page 434),used for giving service over rural power lines and for other purposes (page 434). Of the systems shown, only the types B and G transmit the carrier component.

The various carrier systems have features in common, yet each has distinguishing characteristics. They provide excellent telephone channels, and their importance in comparison with other facilities is indicated by Fig. 19. The types C, J, and K systems listed in Fig. 18 and the type L system are of most importance and will be considered in greatest detail.

Figure 19. Approximate circuit miles of voice-frequency telephone facilities on open-wire toll lines and cables as compared with circuit miles of carrier-frequency toll facilities.