A Single-Sideband Short-Wave System for Transatlantic 



Telephony * 



By F. A. POLKINGHORN and N. F. SCHLAACK 



This paper describes the construction of a short-wave single-sideband 

 reduced-carrier system of radio transmission. It also reports the results of 

 comparisons made between this system and an ordinary short-wave double- 

 sideband system between England and the United States. It was found that 

 the single-sideband system gave an equivalent improvement in radiated 

 power over the double-sideband system averaging 8 db. This is in good 

 agreement with the theoretical improvement to be expected. 



Introduction 



THE single-sideband suppressed-carrier method of transmission 

 has been used to effect economies in the power capacity required, 

 energy consumed, and space in the frequency spectrum on carrier 

 telephone circuits for over fifteen years. On the basis of equal peak 

 amplitudes in a transmitter a single-sideband suppressed-carrier 

 system gives a possible theoretical improvement of 9 db in received 

 signal-to-noise ratio over a double-sideband and carrier system. Six 

 db of this improvement is obtained by omitting the carrier and 

 utilizing the entire available amplitude capacity of the transmitter for 

 the sideband. The other 3 db is obtained by reducing the band 

 width of the receiver to only that required to pass one sideband, thus 

 reducing the noise energy at the receiver output by one-half. 



In order that speech may be transmitted without undue distortion 

 over a single sideband system, it is necessary that the carrier frequency 

 at the receiver be within about ± 20 cycles of the correct value. For 

 the transmission of music a much higher precision is required. The 

 practical construction of a single-sideband radio system at frequencies 

 of the order of 60 kc, such as is used in the long-wave transatlantic 

 telephone circuit, requires only a careful application of known tech- 

 nique to obtain the desired degree of stability of the oscillators. At 

 the short-wave transatlantic radio telephone frequencies of from 5,000 

 to 20,000 kc, however, the very best crystal oscillators, such as are 

 now used only for the very highest quality laboratory standards, 

 would be required at both transmitter and receiver to obtain the 

 degree of synchronization required. 



This high degree of frequency stability can be dispensed with by 



* Published in Proc. I.R.E., July, 1935. 



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