Transatlantic Radio Telephony 1 



By H. D. ARNOLD and LLOYD ESPENSCHIED 



Synopsis: The first transmission of the human voice across the Atlantic 

 was accomplished by means of radio in 1915. Since that time substantial 

 progress has been made in the art of radio telephony and in January of 

 this year another important step was taken in the accomplishment of trans- 

 oceanic voice communication. At a prearranged time telephonic messages 

 were received in London from New York clearly and with uniform intensity 

 over a period of about two hours. 



These talking tests were part of a series of experiments on transatlantic 

 telephony which are now under way, the results of which to date are re- 

 ported in this paper. 



A new method of transmission, radiating only a single side-band, is being 

 employed for the first time. As compared with the ordinary method of 

 transmission, this system possesses the following important advantages: 



The effectiveness of transmission is greatly increased because all of the 

 energy radiated is effective in conveying the message; whereas in the ordinary 

 method, most of the energy is not thus effective. 



The stability of transmission is improved. 



The frequency band required for transmission is reduced, thus conserving 

 wave length space in the ether and also simplifying the transmitting antenna 

 problem. 



An important element of the high-power transmitter is the water-cooled 

 tubes, by means of which the power of the transmitted currents is amplified 

 to the order of 100 kilowatts or more. The direct-current power for these 

 tubes is supplied from a 60-cycle, a-c. source through water-cooled rectifier 

 tubes. 



A highly selective and stable type of receiving circuit is employed. 

 Methods and apparatus have been developed for measuring the strength 

 of the electromagnetic field which is delivered to the receiving point and 

 for measuring the interference produced by static. 



The transmission tests so far have been conducted on a wave length of 

 5260 meters (57,000 cycles per second). The results of the measurements 

 during the first quarter of the year on the transmission from the United 

 States to England show large diurnal variations in the strength of the 

 received signal and in the radio noise strength, as is to be expected, and 

 correspondingly large diurnal variations in the ratio of the signal to noise 

 strength and in the resulting reception of spoken words. Also, the measure- 

 ments, although as yet incomplete, show a large seasonal variation. 



The character of the diurnal and seasonal variations is clearly indicated 

 in the figures. The curves present the most accurate and complete data of 

 this kind yet obtained. 



ON January 15, of this year, a group of about 60 people gathered 

 in London at a prearranged time and listened to messages 

 spoken by officials of the American Telephone and Telegraph Com- 

 pany from their offices at 195 Broadway, New York City. The 

 transmission was conducted through a period of about two hours, 

 and during this time the words were received in London with as much 

 clearness and uniformity as they would be received over an ordinary 

 wire telephone circuit. During a part of the time a loud speaker 



'This paper, with the exception of the Appendix, was presented at the Annual 

 Convention of the A. I. E. E., Swampscott, Mass., June 26-2?, 1923, and was printed 

 in the Journal for August, 1923. 



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