176 BELL SYSTEM TECHNICAL JOURNAL 



the energy for about 300 telephone circuits is transmitted inside this 

 sheath. 



While both the radio and the wire transmission involve similar 

 electromagnetic waves, there could hardly be a greater contrast in the 

 method of handling waves than that between the radio transmission we 

 are considering in this paper and transmission employing such wire 

 methods and spanning the comparable distance of say San Francisco 

 to New York. 



Recently in visiting the short wave receiving station in New Jersey 

 I was shown oscillographs taken on radio telegraph transmission in 

 which each telegraph dot was followed about a tenth of a second later 

 by what appeared to be an echo. The first transmission came some 

 3,000 miles from England. The second transmission had gone the 

 opposite direction around the world and had travelled some 22,000 

 miles before reaching the same receiving point. In such long distance 

 radio we may then have a situation in which each individual signal 

 sets up oscillations, perhaps measurable oscillations, in space surround- 

 ing practically the whole earth. 



Contrast this to the toll cable shown in the picture which, as already 

 noted, contains about 300 circuits. Such cable is used now com- 

 mercially for distances up to around 1,500 miles and is permissible for 

 3,000-mile distances such as we are here considering. In such cables 

 each message is practically confined to a strip of space extending be- 

 tween the terminals of the cable and smaller around than a lead pencil. 

 In the radio case we have literally all out of doors but there is little 

 we can do to control it. In the cable case the channel is reduced to the 

 meagerest dimensions but this so reduced space we can pretty nearly 

 call our own, surrounded and shielded as it is by a sheath and contain- 

 ing carefully balanced circuits. Such space is only occasionally pene- 

 trated by outside disturbances when some of our power friends set up 

 unusually strong electrical fields in its immediate neighborhood. By 

 loading, by amplifiers, by equalization of various sorts, this meager 

 space is guarded and controlled and rendered efficient and constant. 



We are still somewhat in the dark as to how kind nature has been to 

 us regarding short waves and what degree of reliability we can ulti- 

 mately get from a circuit employing them. There is nothing yet in the 

 picture, however, to suggest a reliability for long or short wave radio 

 approaching that of a cable circuit for similar distances. 



A large number of measurements have been made of the strength of 

 the radio fields laid down in England from the long and short wave 

 stations in America and similarly in America from the English stations. 

 Along with such data is taken the amount of noise interference present 



