CHAPTER XI 



RADIO COMMUNICATION 1 



There's music in the air. 



G. F. ROOT. 



All of the inventions of electrical appliances described above 

 that have succeeded one another with such rapidity have been 

 marvelous, but no other one has so taken hold of the popular 

 interest as has wireless or radio. It has seemed incredible and 

 little short of the supernatural, yet it is quite simple and easily 

 comprehensible as science now explains it. 



Transmission of telegraphic and telephonic messages by radio 

 is accomplished by setting up in the ether an electrical wave 

 motion, which, when intercepted by a suitable receiving appara- 

 tus, will in turn set this receiving apparatus into vibration similar 

 to the electrical vibration of the transmitting station. Thus 

 the original dots and dashes or the speech or musical sounds 

 originating at the sending station may be reproduced at the 

 receiving station, sometimes many thousands of miles distant. 

 The ether is a highly elastic medium that is supposed to fill space. 



It must be understood that the actual vibrations in the ether 

 of the space separating the stations are inaudible, and produce 

 sound only after they have set the apparatus of the receiving 

 station into vibration and these electrical vibrations have been 

 converted into less rapid vibrations that produce sound or leave 

 a permanent record, as in the case of automatic recorders. 



Since the whole system of radio transmission depends on 

 wave motion in an elastic medium, it can be compared with other 

 wave motions which are more familiar. Recall how a stone 

 thrown into a quiet pond starts a series of waves that in ever 



1 This chapter has been prepared by Fred G. Anibal, formerly radio officer, 

 U.S. Air Service. 



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