THE L3 SYSTEM — DESIGN 



791 



ducts entered into the determination of signal levels and frequency 

 allocation will be discussed later. 



2.152 Location of the Television Carrier Relative to the Telephone Chan- 

 nel Carriers 



Among the important modulation product types is one formed by 

 difference frequencies involving components of the telephone and tele- 

 vision signals, see Fig. 8(d). These interferences fall back into the tele- 

 phone band and are of different magnitudes depending, among other 

 things, on which components of the television signal produce them; those 



(a) 



(b) 



(c) 



(e) 



(f) 



MESSAGE SIGNALS 



A 

 __f 



TELEVISION SIGNAL 



(d) I lllllll 



FREQUENCY ALLOCATION OF SIGNALS 

 I I I 



I ! I 



llllll|lllli 



TELEVISION 2ND HARMONIC SPECTRUM 

 I (2B, 2C,B+C) I 



mil 



MESSAGE-TELEVISION SUM PRODUCTS 



I CA+B,A+C) ! I 



' I ' 1 



I I I ! 



lli|miiiiii 



llu 



MESSAGE-TELEVISION DIFFERENCE PRODUCTS 



(B-A,C-A) I I 



lllllll|lllll 



ILL 



Xili 



TELEVISION DIFFERENCE PRODUCTS 

 I |(C-B)| j 



'ill 

 I ' I I I 



^ 



lllliiiiiiiiiiiili 



I TELEVISION COMPRESSION 



(3RD ORDER PRODUCTS OF TELEVISION COMPONENTS) 



(g)U 



iiiiiiiiii 



3RD ORDER CROSS PRODUCTS 



(A+B-C,A+C-B) ! 



2 3 4 5 6 7 



FREQUENCY IN MEGACYCLES PER SECOND 



Fig. 8. — L3 coaxial system. Critical modulation products in combined message- 

 television application. 



