Electrical Tests and Their Applications in the Maintenance of Telephone Transmission

T HE installation and maintenance of the circuits in a telephone plant employed for the transmission of speech require 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 having been done the next step is to provide an adequate testing program. A number of the electrical tests required in this program include well known laboratory methods adapted so that they can be readily applied in the field, while others have been developed for particular use in telephone maintenance work. Standard types of test boards and portable testing arrangements are as a rule made up of simple circuits designed electrically and mechanically in a manner to facilitate ready connection to the o erating circuits in the plant. It has been found by experience that many of the transmission 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 development of testing apparatus to meet the additional maintenance requirements. 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 transmission efficiency of the various types of telephone circuits now in general use.