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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



pletely except for those frequencies which are within 500 kc of television 

 carrier. Lower sideband frequencies within 500 kc of carrier are sup- 

 pressed only pa^rtly as also are upper sideband frequencies mthin 500 kc 

 of carrier to achieve a symmetrical response function in the vestigial 

 sideband region. . 



It is convenient in a discussion of vestigial sideband transmission to 

 consider the transmission as made up of two components, each symmet- 

 rical about carrier frequency, a real or in-phase component and a 

 quadrature component which is a distortion term. The process is illus- 

 trated in Fig. 5. Here the response function shown in Fig. 5(a) represents 

 idealized conditions for vestigial sideband transmission. The main side- 

 band is shown extending from carrier frequency Fc to the upper cut-off 

 Fu. A vestige of the lower sideband extends from carrier frequency to 

 the lower cut-off Fv. Constant envelope delay is required in the entire 

 band from Fv to Fu. In the frequency region Fc =b Fv the response 

 characteristic is so shaped that the sum of responses at corresponding 

 frequencies above and below carrier add to a constant value. The sum- 

 ming of signal components in the vestigal bands above and below carrier 

 is accomplished by the receiver demodulator. 



The response function of Fig. 5(a) may be considered to be the sum 

 of the two response functions 5(b) and 5(c) which have even and odd 

 symmetry respectively about the carrier Fc. Both 5(b) and 5(c) are 

 double sideband functions. The component in Fig. 5(b) represents the 



VESTIGIAL 

 SIDEBAND Fv 



(aj VESTIGIAL SIDEBAND RESPONSE FUNCTION 



§olL 



(b) 



REAL COMPONENT 



1 



(C) QUADRATURE COMPONENT 



Fig. 6 — Response function of a vestigial sideband currier system. 



