The L3 Coaxial System 



System Design 



By C. H. ELMENDORF, R. D. EHRBAR, R.H. KLIE, and 

 A. J. GROSSMAN 



(Manuscript received March 31, 1953) 



The L3 coaxial system is a new broadband facility for use with existing 

 and new coaxial cables. It makes possible the transmission of 1,860 tele- 

 phone channels or 600 telephone channels and a television channel in each 

 direction on a pair of coaxial tubes. The principal system design problems 

 and the methods used in their solution are described. The over-all system is 

 described in terms of its components and their location in the system. 



1.0 Introduction 



The L3 coaxial carrier system is a new broadband transmission system 

 capable of transmitting either 1,860 telephone message channels or 

 600 message channels and a 4.2-megacycle broadcast television channel, 

 in each direction, on a pair of coaxials. The system is designed so that 

 signals transmitted over any of these channels will meet high quality 

 Bell System objectives after 4,000 miles of transmission. 



The system is composed of auxiliary or line repeaters spaced at ap- 

 proximately four-mile intervals along the cable route and connecting 

 terminal or dropping repeaters where telephone or television signals 

 are translated to or from the L3 frequency band. Equalization equip- 

 ment, power generating and power transmission equipment, and main- 

 tenance equipment are required at 100 to 200-mile intervals. 



Planning and exploratory development for the system was started 

 late in 1945 with the objective of designing a trunk route system which 

 would provide the maximum channel capacity on the existing coaxial 

 cable consistent with the state of the repeater art. At that time and for 

 the next four years a large amount of new cable employing the 600 

 channel-three megacycle LI coaxial carrier system was being installed 

 or projected.^ 



Since a major field of use of the L3 system was to replace the LI 



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