840 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



ment. This intermediate point is referred to as an equalizing auxiliary 

 repeater. It is provided with the so-called A equalizer consisting in 

 turn of fixed, manual and automatic gain equalizers. It reduces the gain 

 error to less than 0.5 db using the fixed and manual sections and prevents 

 appreciable degradation of this residue during an ensuing three month 

 period by the action of three "office" regulators using pilots at 308, 

 2,064, and 7,266 kc controlling three regulating networks. One of these 

 networks is the V7 shape of the receiving amplifier.^ The other two are 

 first order corrections for vacuum tube aging and repeater temperature 

 changes. 



At offices, (switching main repeaters), on telephone systems further 

 equaUzation is required to permit line switching of telephone channels 

 and special service signals such as telegraph. Also it is not practical to 

 provide telephone equalization on a cumulative basis over longer links 

 than a switching Unk because of frogging and dropping.^ No telephone 

 channel rides for more than 800 miles in the same frequency location 

 and dropping breaks up the pattern still further. Thus, for telephone, 

 the switching links, which may number between 30 and 40 in a long 

 system, are independently equahzed. 



The B equalizer contains manual and automatic sections, the latter 

 being three regulating networks omitted in the A equalizer. Thus an 

 A plus a B forms the final telephone equalization. The residue of five, 

 independently-adjusted AB links must meet telephone requirements 

 without frogging and 30 to 40 links must meet these requirements with 

 800-mile frogging. This performance must continue to be met in the 

 presence of a normal amount of spare line switching. Also it is very 

 important that the character of the residues be such as not to throw 

 an undue burden on the television equalization. 



In combined systems the more stringent requirements require the 

 addition of further manual equalization to the switching section. The 

 residue at the output of a C equalized switching section must be suffi- 

 ciently small that a 4,000-mile circuit will continue to meet television 

 transmission requirements in spite of a normal amount of spare line 

 switching. Also the C equalizer in conjunction with the AB must permit 

 several switching links to be connected in tandem without further line 

 equalization. The C equalization also contains an adjustable delay 

 section which in conjunction with a fixed delay equalizer in the office 

 path provides delay equalization for the television part of the band, 

 3.6 to 8.5 mc. This adjustable section builds out the line to match the 

 fixed unit. 



The A-B-C pattern is for equalization of individual switching lines 



