CF.ki.ii\ in lORS .IFl'F.CTI.W, i i i lA.K.iii i :sfi.i.i > s^i 



best from tfu- slan(l(x>iiit of interference, since it ccmtains tlie least 

 amount of these hiiilier fret|tiencies. 



l-rom the preieilinn it is roncliulecl that fur tlie r.ise uiuier con- , 

 sideration, the wave form C in l'"ig. 1 prodiired hy sending a rec- 

 tangular shapetl signal element through a suitable network is the 

 most suitable. This wave form is almost the optimum from the 

 standpt^int of the received signals while from the standpoint of inter- 

 ference into other circuits it leaves little to be desired. 



I ARRIKR .\ND R.\I)IO 



The results for the distortionless line are particularly applicable 

 to the cases of radio and carrier telegraphy because in these cases 

 we have a transmitting medium which is substantially distortionless. 

 We may again make use of I'ig. 1 to illustrate three possible voltages, 

 it being understood that these cur\es represent the envelope or outline 

 of the transmitted currents which are in reality of a frequency con- 

 siderably higher than the signaling frecjuency. If now we limit con- 

 sideration to the case where the carrier frequency is located in the 

 middle of the transmitted frequency band, then, this case becomes 

 very similar to the direct-current case and what has been said about 

 the received wa\e shape being independent of the transmitted one 

 and its magnitude being directly proportional to the area under the 

 transmitted voltage cur\e still holds. One important difference is 

 that, whereas in the direct-current case the network shown at D, 

 F"ig. 1, is used in the alternating-current case having the carrier 

 located in the middle of the free transmitted range, the network 

 shown at E, Fig. 1, is used. A further difference is that in the case 

 of radio where verv' high frequencies are involved, it may not be 

 practicable to construct the required networks. In that case, how- 

 ever, it is practicable to produce the corresponding direct-current 

 wave and utilize it to modulate the radio wave. 



What was said about interference from the circuit in question 

 into other circuits in the direct-current case above also holds for the 

 case of radio and carrier with the difTerence that whereas F"ig. 2 

 shows a band of frequencies extending from zero up, the corresponding 

 curve in the case of radio and carrier consists of two such bands. 

 The complete curve for radio and carrier is substantially symmetrical 

 with respect to the ordinate corresponding to the carrier frequency, 

 and the right-hand portion is similar to the curve shown in Fig. 2. 

 It will be obvious that the rectangular wave and the half-cycle sine 

 wave are both objectionable, as voltage waves to be applied to the 



