TRANSATLANTIC RADIO TELEPHONY 249 



10 kw. of power. It was decided that about 20 of these tubes were 

 as many as could be reasonably expected to work satisfactorily in a 

 parallel combination. In order to use these powerful tubes in the 

 most advantageous and economical way, the transmitter was con- 

 structed to radiate what is called a single sideband carrier eliminated 

 transmission. 



In the ordinary radio telephone transmission such as is used in 

 broadcasting, the radiation sent out consists of a carrier frequency 

 together with two sidebands. The carrier transmits no intelligence 

 but the complete message is transmitted in duplicate since each side- 

 band contains the entire message. By eliminating one of the sidebands 

 and the carrier it is possible to send out the intelligence using only 

 one sideband. If the entire power capacity of the transmitting 

 system is thus concentrated on a single sideband, the power is used 

 several times more effectively. 



Since it is more difficult to filter a single sideband away from its 

 carrier and its brother sideband as the frequency becomes higher it 

 was decided to produce the single sideband at a relatively lower 

 frequency as is done in wire carrier telephony and then step it up by 

 a modulation process to the desired position in the frequency range. ^ 

 The voice was therefore modulated upon a 30-kilocycle carrier, and 

 the single sideband produced by passing the modulated result through 

 a band pass- filter. This band is then combined in a second modulator 

 with a frequency of 90 kilocycles and the resulting difference frequency, 

 which is a sideband at 60 kilocycles, after passing through another 

 band filter is ready to be amplified to high power for radiation from 

 the antenna. Four preliminary stages of amplification are necessary 

 before the final high power 20-tube amplifier is reached.^ 



When this transmitting apparatus first became available for experi- 

 mental trial, it was set up at the large radio station at Rocky Point, 

 Long Island, since the experiments were at that time being made in 

 cooperation with the Radio Corporation of America, and the Radio 

 Corporation arranged to lend one of its large and efficient antennas ^ at 

 that station. Subsequently this antenna was leased for use in the 

 final experiments and in giving a commercial service. 



^"Production of Single Sideband for Transatlantic Radio Telephony," R. A. 

 Heising: Proceedings of the Institute of Radio Engineers, Vol. 13, No. 3, June 1925, 

 pp. 291-312. 



' "Power Amplifiers in Transatlantic Radio Telephony," A. A. Oswald and J. C. 

 Schelleng: Proceedings of the Institute of Radio Engineers, Vol. 13, No. 3, June 1925, 

 pp. 313-361. 



^ For a description of this type of antenna known as a multiple tuned antenna see 

 "Transatlantic Radio Communication," E. F. W. Alexanderson: Proceedings of the 

 American Institute of Electrical Engineers, Vol. XXXVIII, Part II, 1919, p. 1089. 



