118 BELL SYSTEM TECHNICAL JOURNAL 



to a transmission background, as it were, which is common to both 

 arts. 



The engineering handhng of the transmission problems which arise 

 from these fundamental communication requirements has been quite 

 highly developed in the older of the two arts — ^wire transmission — in 

 connection with telephone repeaters and carrier telephone and tele- 

 graph systems. It should be, therefore, interesting and profitable 

 to apply some of the transmission technique thus developed in the 

 wire art to several of the more important radio problems. In so 

 doing, we obtain rather new viewpoints of radio transmission and a 

 useful correlation of it with the better established wire methods. It 

 is hoped, therefore, that the picture which is presented of radio and 

 wire transmission, treated from a common standpoint, may con- 

 tribute to a better appreciation of both arts by radio and wire engineers 

 alike and may make clear the underlying transmission principles 

 which are common to them. 



Principal among the problems of electric communication is the one 

 of delivering at the receiving end the required volume of signal with 

 the necessary freedom from interference. The delivering of the 

 required volume is a matter of overcoming the transmission losses 

 of the system by amplification; while the obviating of interference is, 

 of course, concerned with the reduction of the ratio of the interfering 

 to the signaling energy. 



Transmission Losses 



In considering these factors we will take up first the primary one 

 of the losses which are suffered by the carrier waves as they are 

 propagated thru the transmission medium. In both wire and radio 

 transmission, of course, the actual propagation of the electromagnetic 

 wave energy occurs in the "ether," the difference being that in the 

 wire case, the waves are bound to a guiding path, whereas in the radio 

 case they are transmitted freely in all directions and bound merely 

 to the earth's surface. This difference in the mechanism of trans- 

 mission gives rise to an important difference in the transmission 

 losses occurring in the two cases. In order to assist in visualizing the 

 two cases they are indicated diagrammatically in Fig. 1. 



Referring first to the wire case, the law in accordance with which 

 the current and voltage strength decrease as the transmission wave 

 travels along the wire, is the familiar one of attenuation. 



/ie-«' = h, (1) 



