THE L3 SYSTEM — DESIGN 809 



equalizer shapes to correct for the second order effects of temperature 

 changes and electron tube aging. Also under active study are the prob- 

 lems associated with final mop-up for long television systems. 



3.0 System Description 



3.1 general 



In the preceding sections on system design the functions of the aux- 

 iliary repeaters and the need for additional repeaters with varying 

 amounts of equalization have been brought out. Fig. 14 shows the trans- 

 mission layout of a typical L3 system. The auxiliary repeaters contain 

 amplifiers and regulating equipment to compensate for the basic cable 

 loss and its variation with temperature. Since such repeaters are de- 

 pendent on the cable for their primary source of power they are called 

 auxiliary repeaters. 



At points in the system where additional first order equalization is 

 required to reduce misalignment the complexity of the repeater equip- 

 ment increases and such repeaters receiving power over the cable are 

 called equalizing auxiliary repeaters. 



The distance which power may be transmitted over the cable to the 

 auxihary repeaters is limited; therefore, repeaters at specified intervals 

 must be capable of supplying power to the cable. These are called main 

 repeaters. They may be equalizing main repeaters where only first- 

 order equalization is required or switching main repeaters where lines 

 are switched or circuits dropped. 



3.2 AUXILIARY repeater 



3.21 Transmission Circuit 



The auxiliary repeater is the basic unit of the system and its design 

 determines to a great extent the performance and economics of the 

 system. A block diagram of such a repeater for transmission in two 

 directions on two coaxials is shown in Fig. 15. The power separation 

 filter (PSF) is a six terminal high pass-low pass filter designed to sepa- 

 rate the high frequency transmission signals on the coaxial from the low 

 frequency current transmitted on the center conductor to furnish pri- 

 mary power to the repeater power equipment. At the input to the repeater 

 the low-frequency current is diverted to a power supply while the high- 

 frequency current follows a path through passive networks to the input 

 of the amplifier. At the output, the signal from the amplifier and the 

 low-frequency current from the power supply are recombined in the 

 power separation filter for transmission to the next repeater. 



