OVERSEAS RADIO EXTENSION 261 



tennas sharp in the vertical plane, which have given as much as 16 to 

 20 db gain over a one half wave vertical antenna on local test but 

 which have given for a signal from a distant point all variations of 

 gain from this same value down to a loss of 2 db. 



Planning the International Use of Frequencies 



The problems of the transmitting medium discussed above are 

 those which have been under study in connection with telephone 

 transmission across the North Atlantic and between North and South 

 America. Doubtless further observation and the exploration of other 

 portions of the earth's surface will disclose a much more complete 

 picture than it is now possible to present. It is important that fur- 

 ther data be gathered not alone for the purpose of improving the 

 transmission results obtained but also for use in agreeing interna- 

 tionally upon the most effective use of the frequency spectrum for 

 different services in the interest of the world as a whole. 



Of fundamental importance is the question of the frequencies which 

 are best suited to different distances of transmission. The curves of 

 Fig. 11 ^ give this relationship between frequency and distance in so 

 far as it has been disclosed by measurements carried on between North 

 America and Europe and South America, and also between the Ameri- 

 can continent and ships plying the Atlantic Ocean. In the construc- 

 tion of these curves use has been made also of data obtained by other 

 agencies such as the Radio Corporation and the United States Navy 

 Department. The curves are reproduced here merely for such use 

 as they may be in connection with this problem of planning and with 

 the hope of stimulating the contribution of corresponding data for 

 other regions of the earth. It should be realized that actually each 

 curve is the center of a considerable band of frequencies and that 

 these bands merge one with another. 



While experience has indicated that during the adverse transmission 

 conditions which accompany a magnetic storm some improvement 

 in transmission can at times be obtained by shifting the frequency. 

 In general, these effects are found to extend over the entire high- 

 frequency range now in general use, and shifting frequency does not 

 dodge them. 



In view of the extent to which transoceanic radio links, telegraph 

 as well as telephone, are dependent upon the use of the higher fre- 

 quencies, and of the importance of communications to the world as 

 a whole, it is highly desirable that they be conserved for these longer 

 distance uses. This has already gained recognition and the 1929 



'• See bibliography 12. 



