592 BELL SYSTEM TECHNICAL JOURNAL 



Staggering of Frequency Bands. A substantial reduction of crosstalk 

 is obtained through the staggering of an adjacent system frequency 

 allocation as previously noted. Figure 5 shows the frequency 

 allocations of the C-N and C-S systems. Because present standard 

 types of telephone transmitters and receivers have response charac- 

 teristics which exhibit the greatest sensitivity in the vicinity of 1,000 

 cycles, as the bands of two adjacent channels are shifted from an over- 

 lapping position, the crosstalk is appreciably reduced. In this case 

 also the overlapping crosstalking points are always opposite side- 

 bands and the intelligibility is completely lost even for the case of a 

 substantial overlapping. 



It is customary to install C-N and C-S systems on the two side 

 circuits of a phantom group. The phantom group comprises four 

 wires which are most closely associated electrically because they are 

 employed not only to provide a telephone circuit on each pair of 

 wires but a phantom telephone circuit each side of which is comprised 

 of one pair of wires in parallel. 



A typical arrangement of facilities afforded by one crossarm of the 

 telephone line is illustrated by Figure 16. It will be noted that this 



OOO AAAAA OOO GOG 



• • • • 



^ 6i ^ 6« sB] i_6! i6 iB !B ^ 



Phanlomed 



with liiair ISfie on 



next crossarm 



T0TAL5 

 LEGEND TELEPHONE TELEGRAPH 



• VOICE FREQUENCY TELEPHONE CIRCUIT 7.5 



O CARRIER TELEPHONE CIRCUIT \Z 



A GROUNDED DC TELEGRAPH CIRCUIT 10 



A CARRIER """ELEGRAPH CIRCUIT 10 



19 b lo' 



Figure 16 — Arrangement of communication facilities on one crossarm 



crossarm provides a total of twelve carrier telephone channels, five 

 regular telephone circuits, two and one half phantom circuits, thus 

 making a total of nineteen and one half telephone circuits. The 

 telegraph facilities would total ten regular grounded d.-c. telegraph 

 circuits, one for each wire, and ten carrier telegraph channels on the 

 pole pair, thus affording a total of twenty duplex telegraph channels. 

 This is, therefore, an average of approximately four telephone channels 

 and four telegraph channels per pair of wires, which is obviously a 

 fairly efficient use of the copper wire. 



