Transatlantic radio telephony

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 transoceanic 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 recent talking tests were part of a series of experiments on transatlantic telephony which are now under way, the results of which to date are reported in the 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 t- e 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 measurements, 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.