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BELL SYSTEM TECHNICAL JOURNAL 



equalizer is to be associated with and also include a fixed amount of 

 high-frequency attenuation correction. 



On Fig. 5 is shown a schematic diagram of one of the low-frequency 

 attenuation equalizers. This consists of four sections of 600-ohm 

 constant impedance type networks. One section referred to as a basic 

 section introduces attenuation correction over the complete frequency 

 range from 35 to 8,000 cycles for a particular minimum length of line, 

 as for example, in the case of 165-mil circuits this is for 100 miles. 

 The three other sections on the other hand furnish attenuation correc- 

 tion only for frequencies from approximately 1,000 cycles down to 

 35 cycles. Section 1 of the equalizer for 165-mil circuits puts in about 

 }/2 db more loss at low frequencies than it does at 1,000 cycles. Sec- 

 tion 2 puts in double the amount of correction that is introduced by 

 Section 1 and Section 4 introduces four times as much attenuation 

 correction as Section 1. These three sections are controlled by 

 switches so that any one or all of them may be cut in tandem with the 

 basic section. The attenuation corrections afforded for the various 

 adjustments of this equalizer are shown on Fig. 6. 



Q 4 



30 50 100 500 1000 5000 10,000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 6 — Attenuation correction furnished by low-frequency equalizer for 165-niil. 



circuits. 



The attenuation equalizers for 128-mil and 104-mil facilities are 

 similar in construction to the one just described having different 

 constants so as to furnish somewhat different attenuation correcting 

 characteristics. 



Figure 7 shows a schematic diagram of the high-frequency attenua- 

 tion equalizer. This consists of four 600-ohm constant impedance 

 type network sections which, as indicated, are controlled by switches 

 so that any one or all of them may be cut in tandem with the program 



