2S HELL SySTF.M TECIISICAL JOIRX.IL 



with lelcpljonc repeaters and three, circuits equipped for carrier 

 operation. The latter two classes are alike in many respects as far as 

 the maintenance nietluHls are coiicerne<l and both require somewhat 

 more attention than the circuits not equipixxi with amplifying 

 apparatus. The length and numlx^'r of repeaters involved are also 

 imixirtani factors which must he taken account of in tandem repeater 

 and carrier circuit maintenance. Wry long tandem repeater circuits 



Fig. 1 — Illustrjtiun of 4-.\ Transmission .Measuring Set and 4-B Oscillator Installed 

 in a Toll Test Room 



such, fur ex.imple, as the long toll cable circuits described by Clark- 

 ref|uire s[H'cial maintenance procetlurcs similar in many respects to 

 those re<iuire<l in carrier maintenance. 



The l-.\ t\|H- of transmission measuring set generally used for 

 testing toll circuits may be considered as a toll transmission test 

 desk. Fig. 1 shows a |)icture of one of the latest models together 

 with an oscillator for supplying the measuring current, installed at 

 a toll ortice for use in routine testing. The set is provided witli 

 trunks to both the toll testboard and toll switchboard, and also 

 with call circuits to toll o|K?rators' positions for use in ordering up 

 circuits for test. The electrical measuring circuit is designed so that 

 tests may l)e made on two toll circuits loopetl at the distant end, or 

 str.ii;;hi.iw.i\ on one loll circuit the distant terminal of which termi- 



