WORLD-WIDE TELEPHONY 



495 



Radio Links 



All of the existing intercontinental circuits make use of radio for 

 the long transoceanic jumps, and it seems desirable first to consider 

 the technical problems of radio telephony. 



LONG WAVES MEDIUM WAVES 



LONG MEDIUM DISTANCE 



DISTANCE INCLUDE BROADCASTING 



SHORT WAVES 

 LONG DISTANCE 



ULTRA SHORT WAVES 

 SHORT DISTANCE 



FREQUENCY IN CYCLES PER SECOND 



WAVELENGTH IN METERS 



Fig. 7 — Radio frequency chart. The bands applicable to intercontinental service are 

 indicated by shaded areas. 



Fig. 7 shows the radio spectrum with an indication of the uses made 

 of the various portions of the spectrum. Only the two shaded parts 

 of this spectrum appear to be applicable to intercontinental telephony. 

 One, in the long wave range, extends from about 15 kilocycles to per- 

 haps 100 kilocycles. The second includes the short-wave range from 

 about 6000 to 23,000 kilocycles. 



The transmission of these two wave ranges exhibit interesting 

 differences in characteristics. For the short wave-lengths the trans- 

 mission is frequently referred to as being in the form of "sky waves." 

 This is for the reason that at intermediate distances the waves may 

 practically disappear near the surface of the ground but reappear at 

 greater distances. They appear to have been carried around the 

 curvature of the earth's surface by refraction or reflection from ionized 

 atmospheric layers. While the action in the long-wave range at 

 great distances appears to be also conditioned partly by the ionized 

 layers, the field at the surface of the earth falls oft' continuously as the 

 distance from the transmitter is increased. 



Interesting results are now being obtained in the use for communi- 

 cation purposes of very short radio waves having frequencies above 

 30,000 kilocycles. The work done to date indicates that these fre- 

 quencies are not sufficiently deflected from their paths by the at- 

 mosphere to follow the earth's curvature. This characteristic 

 appears to prevent the use of these very short radio waves for direct 

 transmission over long distances and limits direct transmission to 

 distances so short that the earth's curvature is not a large factor. For 



