The Receiving System for Long-Wave Transatlantic Radio Telephony

A R L Y in October, 1915, engineers of the Bell System stationed in Paris heard the words "good night Shreeve," which had been transmitted from Arlington. T h a t 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 nondirectional 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 development of the vacuum-tube amplifier, however, the following considerations each became important, especially so for a telephone circuit: 1 Published in Proc. of I. R. E., Dec., 1928, pp. 1645-1705. 309 310 BELL SYSTEM TECHNICAL JOURNAL 1. The signal-to-noise ratio at the receiving location, which in turn is dependent upon four factors-- (a) The efficiency of the transmitting set, (b) The efficiency of the transmitting antenna, (c) Attenuation in the radio path, (