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BELL SYSTEM TECHNICAL JOURNAL 



present instance, the sending-end current is usually characterized 

 by peaks and rapid changes, while the received wave is somewhat 

 rounded off, and this results in most of the induction taking place 

 in tlie portion of the line near the sending station and the apparatus 

 at that station. C illustrates sending-end crossfire between wires 

 of the same pair and D that between wires of different pairs but in 

 the same quad. Trace E shows the receiving-end crossfire between 

 wires of the same pair and F that between wires of different pairs 

 but in the same quad. C, D, E, and F may be considered as super- 

 posed in various comi)inations on B to obtain an idea of the mutila- 

 tion of signal wa\es at usual speeds of manual Morse operation. 



Marking 



bpacmg 



Crossfire impulse 



Distorted 

 Signal 



Fig. 3 — Distorting effect of crossfire impulse 



Fig. 3 has been drawn to illustrate how a crossfire impulse may 

 cause distortion of a telegraph signal. The lowest wave is a combina- 

 tion of the received signal and crossfire impulse which are shown 

 above. X and Y are the points at which the polar relay operates, 

 assuming that it is required that the current build up or down ap- 

 preciably beyond zero in order to move the armature. It will be 

 clear that the dash has been shortened by the amount Z. Obviously 

 only a limited amount of such distortion is allowable in telegraph 

 signals. Under some conditions the crossfire is of sufficient strength 

 to cause false signals, such as an extraneous dot in a long space or 

 a break (space) in a dash. 



