42 /'/:/./. .V)\/7;A/ IICIIXIC.II. JiH KS.II. 



niissidii, aixl l.itiT llio fe.iturcs iit this coniurlioii iudr- parliciilailv 

 UkMitiru"*! with tflfphoiic ri'iH-Miors and i-arrier s\slems arc discussed. 

 The difTereiU elassi's i)f i-ircuits i^ixcn in Tahle I arc made up of 

 various comliinalions of tlic following indiviihial parts: 



The above parts are coinl)ined in various ways to make up the com- 

 plete (i|)erating circuits such as cord circuits, operators' circuits, 

 trunk circuits, etc. Kach complete circuit causes a definite normal 

 loss to telephone transmission which must he taken accoinit of in 

 designing the plant to meet the \'arious service requirement^. If, 

 howe\er, any of the parts used are defective, if the wrong combina- 

 tions of parts are nsetl, or if the installation work is not correciK- 

 done, excess transmission losses will result which may very seriousK- 

 affect the transmission when the particular circuits inxotved arc 

 employed in an overall connection. 



Classification of Common Types of Troubles. An anahsis of a 

 large amount of transmis.sion testing data has made it possible to 

 develop a definite trouble classification which is particularly helpful 

 in transmission maintenance work and which permits the most 

 efficient use of the results in eliminating transmission troubles, llx- 

 jHTience has shown that the troubles found can be divided into two 

 general classes. A— troubles which can be detected either by .siiiiplt> 

 d-c. or a-c. tests in connection with the regular day-by-day main- 

 tenance work or by transmission measuring sets, and B — troubles 

 which can be detected most readily by transmission measuring sets. 

 The most important troubles in the abo\e classes are as follows: 



Claw A Class B 



If, in m.iking ir.insnii^ion tests in a cent ml office, a liigii pcr- 

 cent.igeof ("l,iss A troubles is found the remedy isgener.illy to instigate 



