THE L3 SYSTEM — EQUALIZATION AND REGULATION 841 



and these equalizers are adjusted on a single switching link basis. On 

 the office side of the switches are system components that also require 

 equalization. In the telephone system these include such things as office 

 cabling and hybrid coils. Also there is an office flat loss of nearly 30 db. 

 Thus the lines are, in effect, operated to give a 30 db gain while the 

 offices give a 30 db loss. Aside from the flat losses there are distortion 

 shapes but fortunately these are all well approximated by a Vj shape 

 and a single manually adjustable v? equalizer plus suitable choice of 

 flat loss provides adequate telephone office equalization. This is referred 

 to as the equalizer. It is adjusted to make the particular office have a 

 flat characteristic. 



In the office circuits of combined systems are branching filters to 

 separate the telephone and television bands. The equalizer is reused 

 in the telephone path. The television path includes the fixed delay 

 equalizer and a manual gain equalizer to correct for office cables, hybrids 

 etc. After the tandem combination of several independently equalized 

 lines and offices further equalization will be required. This will be ac- 

 complished by a multi-control manual D equalizer, having both gain 

 and delay sections, inserted in the television only path at approximately 

 400-mile intervals. These D equalizers will be used to form 800-mile 

 pilot links which are independently equalized to a degree permitting 

 putting any five such links in tandem to form a 4,000-mile circuit with- 

 out further equalization. 



FIXED EQUALIZERS 



The line amplifier can properly be considered as the first step of fixed 

 equalization.^ Also acting at this same level are artificial cable networks 

 used to build out the repeater spacing to 4 =t 0.2 miles, as well as the 

 basic equalizer of the amplifier to take up differences between cable 

 t3rpes. These devices are described in a companion paper. The final 

 step of fixed equalization is the so-called ''design deviation equalizer" 

 associated with all A equalizers. This equafizer comes in two versions, 

 one for use with sections containing 23 to 32 repeaters and one for use in 

 sections of 10 to 22 repeaters. In those few cases of less than 10 repeaters 

 the fixed equalizer is omitted. 



The function of the design deviation equalizer is, first, to correct for 

 the design error of the average repeater and second, to recenter the 

 manual (cosine) equalizers. Although the average repeater matches its 

 four miles of cable to within ±0.12 db this design error accumulates to 

 over 3 db in 30 repeaters and further the shape is a difficult one to equal- 

 ize. In order to keep the number of designs to a minimum only two sizes 



