The Receiving System For Long-Wave Transatlantic 

 Radio Telephony ^ 



By AUSTIN BAILEY, S. W. DEAN, and W. T. WINTRINGHAM 



Transmission considerations and practical limitations indicate that in 

 the lower frequency range, frequencies near 60 kc are best suited for trans- 

 atlantic radio-telephone transmission. A radio receiving location in Maine 

 gives a signal-to-noise ratio improvement over a New York location equiva- 

 lent to increasing the power of the British transmitter about 50 times. 



Various types of receiving antennas are briefly discussed. The wave- 

 antenna is selected as being most suitable for long-wave radio telephony. 

 The various factors affecting wave-antenna performance and methods for 

 measuring the physical constants of wave-antennas are discussed in detail. 

 High-frequency ground conductivities determined from wave-antenna meas- 

 urements are given. Combination of several antennas to form arrays is 

 found to be a desirable means of decreasing interference. The use of a wave- 

 antenna array in Maine decreases the received noise power by an additional 

 400 times. If the receiving were to be accomplished near New York using 

 a loop antenna, we would have to increase the power of the British trans- 

 mitting station 20,000 times to obtain the same signal-to-noise ratio. Com- 

 parisons of calculated and observed directional diagrams of wave-antennas 

 and wave-antenna arrays are presented and discussed. 



The transmission considerations governing the design of a radio receiver 

 for commercial telephone reception are outlined. 



Mathematical discussions of the wave-antenna, antenna arrays, quasi- 

 tilt angle, and probability of simultaneous occurrence of telegraph interfer- 

 ence are given in the appendices. 



EARLY in October, 1915, engineers of the Bell System stationed 

 in Paris heard the words "good night Shreeve," which had been 

 transmitted from Arlington. That date then marks the inception of 

 transatlantic radio-telephone receiving. The progress which has been 

 made in the radio-telephone receiving art since these first experiments 

 is demonstrated by contrasting the homodyne receiver and the non- 

 directional antenna then used with the present commercial receiving 

 system employing double-demodulation of single side band signals 

 and an extensive array of wave-antennas forming a highly directional 

 system. In the pages which follow we shall endeavor to give some 

 of the engineering considerations upon which the design of the present 

 receiving system was based. 



Choice of Frequency 



In the early development of long-distance radio telegraphy, the 

 strength of the received signal was the principal factor upon which the 

 selection of the operating frequency was based. After the develop- 

 ment of the vacuum-tube amplifier, however, the following considera- 

 tions each became important, especially so for a telephone circuit: 



1 Published in Proc. of I. R. E., Dec, 1928, pp. 1645-1705. 



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