CARRIER SYSTEMS ON TELEPHONE LINES 



605 



therefore, reduces the possibility of inter-system crosstalk between 

 carrier systems within the same ofifice. The crosstalk requirements in 

 an office may be more severe than on the pole lines because the level 

 difference between circuits which operate on different pole lines 

 terminating at the same office may be as much as 50 TU. As an aid 

 in obtaining the required electrical separation all high-frequency 

 wiring is reduced to a minimum by segregating and mounting together 

 all line equipment associated with a single circuit. No high-frequency 

 circuits appear at the toll testboard. The toll lines may be tested 

 from the testboard by means of trunks between the testboard and the 

 line equipment bays. All the carrier equipment is thoroughly shielded 

 in such a manner that the separation between the equipment of any 

 two systems is 120 to 135 TU. 



The carrier line equipment at a carrier repeater station is generally 

 similar to that at the terminal stations, as previously shown in Figure 

 26. At each repeater station, however, this equipment is provided in 

 the lines in both directions. Two types of low-pass line filters are 

 employed at the repeater station, one adapted to circuits in which 

 both carrier and voice-frequency repeaters are used and the other, 

 which is less commonly used, for circuits employing only carrier 

 repeaters and where the voice circuit continues through without a 

 repeater. 



Voice- Frequency and Signaling Equipment. The general function of 

 the voice-frequency terminating equipment is to associate, by means of 

 a hybrid coil and network, the ordinary two-wire circuits in the tele- 



Figure 27 — Schematic of voice-frequency circuit for type "C" carrier 

 telephone system 



phone switchboard, including both talking and signaling functions, 

 with the sending and receiving branches of each of the different 



