594 BELL SYSTEM TECHNICAL JOURNAL 



the destination of the voice circuits and with a minimum impedance 

 irregularity for either circuit. These Hne filters are sometimes mounted 

 on poles, so that this transfer may take place where lines join at an 

 outside point and where office equipment cannot be installed. A 

 circuit arrangement illustrating the use of the pole-mounted high-pass 

 transfer filter set is shown in Figure 17. 



Equipment Problems and Typical Installations 



The increasing use of carrier telephony as a substitute for line 

 construction in providing toll facilities on long circuits has, like the 

 development of toll cables, resulted in further increasing the proportion 

 of the plant investment represented by the equipment within the 

 ofifices. It has likewise required that a greater part of the maintenance 

 effort involved in taking care of a given number of facilities be devoted 

 to the equipment. These factors have made the design and arrange- 

 ment of the carrier equipment matters of considerable importance. 

 Recent developments in these respects have, therefore, been directed 

 toward obtaining a high degree of adaptability of the carrier equipment 

 to practical use in the telephone plant. Economies in design have 

 also resulted which have been an important factor in extending the 

 usefulness of the equipment. 



The type "C" carrier telephone equipment is mounted on panels 

 employing a uniform dimensional system in a manner similar to the 

 other recent telephone developments. Arrangements have been de- 

 vised so that in the future this mounting method will permit the 

 desired close association between the carrier filters and other related 

 apparatus in the lines in order to minimize high-frequency losses and 

 impedance unbalances within the ofihces. Signaling arrangements 

 flexibly adapted to present plant conditions have been provided. 



The high frequencies and power levels used in carrier telephony 

 and the frequency conversion functions of the system are the principal 

 electrical factors which affect the arrangement and amount of equip- 

 ment involved. The high frequencies necessitate careful wiring, 

 shielding, and location of certain units with respect to others to avoid 

 undesirable inductive and impedance effects. The modulation and 

 demodulation processes and the high energy levels required necessitate 

 the use of numerous vacuum tubes, with the consequent need of 

 suitable sources of power. 



Typical System Equipments. As noted previously, a long carrier 

 telephone system involves equipment at a number of intermediate 

 repeater stations in addition to that at the terminals. Figure 18 



