The Bell System Technical Journal 



July. 1924 



Electrical Tests and Their Applications in the 

 Maintenance of Telephone Transmission 



By W. H. HARDEN 



Introduction 



THK installation and maintenance of the circuits in a telephone 

 plant employed for the transmission of speech retiuire the use of 

 various testing schemes to insure a high grade of commercial service. 

 Circuits are engineered and installed to meet the established standards 

 of transmission in the most economical manner and this ha\'ing been 

 done the next step is to provide an adeciuate testing program. A 

 number of the electrical tests required in this program include well 

 known lal)orat<)r>' methods adapted so that they can be readily ap- 

 plied in the field, while others have been developed for particular use 

 in telephone maintenance work. 



Standartl types of test boards and porlabli- testing arrangements 

 are as a rule made up of simple circuits designed electrically and 

 mechanically in a manner to facilitate read\' connection to the o. cr- 

 ating circuits in the plant. It has been found by experience that 

 many of the transmissif)n maintenance requirements can be taken 

 care of by direct current testing methods and the simpler alternating 

 current tests. With the advent of vacuum tubes, some of the more 

 complex circuits such as repeaters and carrier called for the develop- 

 ment of testing apparatus to meet the additional maintenance require- 

 ments. Fortunately, the vacuum tube furnished the means whereby 

 new testing devices have been provided which can be applied as 

 quickly and readily to maintenance work as the simpler methods. 



In what follows is given a discussion of the more important electrical 

 testing methods together with the application of these methods in 

 maintaining the transmis.sion efficiency of the various types of tele- 

 phone circuits now in general use. Direct current testing methods 

 arc covere<l first and later alternating current methods are considered. 

 A typical toll connection is used to illustrate the general scheme of 

 applying the various electrical tests in everyday installation and 

 maintenance work. 



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