572 



BELL SYSTEM TECHNICAL JOURNAL 



circuits forming the network but also at all points at which tele- 

 photograph stations are connected. 



A single line schematic of the type of bridging network employed 

 is shown in Fig. 15 (upper left), and a more complete representation of 

 a portion of the network used on cable circuits is shown in Fig. 15 

 (lower right) . Current entering the bridge, for example at the West 

 input, traverses three direct paths of equal attenuation and leaves at 

 East output and branch A and branch B outputs. There are, of course, 

 numerous indirect paths between the West input and each of the bridge 



branch"b" 



OUTPUT 



BRANCH A 

 OUTPUT 



,, J BRANCH "A" 

 I Y OUTPUT 



ONE-HALF OF NO. 44 A I 

 REPEATER OR MODIFIED 

 TWO-WIRE REPEATER 



Fig. 15 — Single line diagram of cable and open-wire bridging networks (upper left) 

 and portion of cable bridge showing arrangement of resistances (lower right). 



outputs; for example, there are two parallel paths to each output. 

 Each of these two paths has three times the attenuation of a direct 

 path and the current through it is 180 degrees out of phase with that 

 through a direct path because of the reversals shown in the wiring. 

 However, the aggregate of all of the indirect paths does not appreciably 

 alter the loss between input and output of this bridge as calculated 

 by neglecting them. It may be noted that the two directions of 

 transmission for the same circuit are connected by six parallel paths 

 each of which has three times the attenuation of a direct path be- 

 tween an input and output of the bridge. The currents through three 



