EFFECT OF SIGNAL DISTORTION IN MORSE TELEGRAPHY 271 



mitting relay Di and passed over the first section of artificial line to 

 the polar receiving relay D^. From D-i the signals were repeated 

 directly into the second section of artificial line and operated the polar 

 receiving relay D^. The latter relay repeated the signals into another 

 local circuit where they were received by the neutral relay Di. The 

 neutral relay repeated the signals in polar form to the transmission 

 measuring set and also to the polar relay D^. The latter relay oper- 

 ated two neutral sounders which were located near the two receiving 

 operators. 



3. Method of Introducing Distortion 



Bias was introduced into the circuit by passing a direct current 

 through winding Wo of relay A- The direction of this current could 

 be reversed by means of the switch 5'PF which was arranged to connect 

 either a positive or a negative battery to the relay winding. Conse- 

 quently, either a positive or a negative bias could be introduced, the 

 amount being controlled by means of the variable resistance Ro. For 

 amounts of bias greater than about 35 per cent the bias was introduced 

 in two sections, by connecting winding Wi of relay Dz in series with the 

 winding Wo of relay Do. This change was found necessary to prevent 

 failure of the system whenever large amounts of bias were desired. 



Negative characteristic distortion was introduced by means of the 

 condensers C2 and G. By increasing the value of capacity in these 

 condensers, any desired amount of distortion up to about 70 per cent 

 could be introduced into the circuit. The effect produced by the con- 

 densers is similar to that caused by the capacity to ground of a long 

 cable circuit, or of intermediate composite sets and similar apparatus 

 having condensers connected from the line wires to ground. 



Positive characteristic distortion was introduced by means of 

 transient currents in a circuit into which was connected a separate 

 winding of one of the receiving relays. The currents flowed through 

 the winding in such a direction as to tend to hold the relay armature 

 against the particular contact to which the armature had been operated. 

 The circuit consisted of the relay winding Wi, the resistance Rz, and 

 the condenser C4, connected in series from the armature of relay D^ to 

 ground. By increasing the values of resistance and capacity to a 

 sufficient extent the duration of the charging current could be made 

 appreciably long. Consequently, a reversal of current in winding Wz, 

 due to the telegraph signals was not able to operate the relay armature 

 to the opposite contact until the condenser d had become sufficiently 

 charged so that the charging current, which flowed through winding 

 Wi, was reduced to a value below that of the line current. The time 

 constant of the holding circuit was such that the amount of charge on 



