sou/:' ihhv i.oxg rr.i.r.riioxr. cincrns 505 



vision of tpsts and adjustments riH|iiirt'd on tht,- circuit as a whole. 

 In addition to the duties in connection willi the maintenance of th<', 

 circuit as a whole each olTice alonj{ the circuit is responsible, of »-oursc, 

 for the proper physical maintenance of the plant in its territorv'. 



High grade maintenance is necessary to reduce to a minimum, 

 service interru()tions, noise and crosstalk and fluctuations in circuit 

 characteristics and equivalents. .An important part of this work 

 consists of fret|uent periwiic inspections, measurements ' of insulation 

 resistance, loop resistance, resistance balance, transmission, noise and 

 crosstalk and equipment parts which are subject to variation. 



In order to make many of the measurements and tests it is neces- 

 sar>' to remove the circuit from service. This would result in con- 

 siilerable lost circuit time if each of the stations made such measure- 

 ments and tests independently. In order to minimize this lost circuit 

 time, therefore, it has been found desirable in the case of long tck>- 

 phone circuits of this type to institute what is known as "co-ordinated 

 testing" procedure. Under this procedure a definite time is set aside 

 for the periodic tests and all repeater stations and both terminal 

 stations co-ordinate their work under the direction of the controlling 

 office. The success of this system is dependent upon each station 

 doing its part of the work correctly and within a specified time al- 

 lowed for each test. The method of conducting the tests is illustrated 

 in the following description. 



1. Roll Call — The tester at the controlling office first calls the roll, 

 starting with the first station and proceeding through to the 

 distant terminal, each station repl>ing b\- name and giving the 

 temperature and weather conditions. 



2. Repeater Amplification and Vacuum Tube Tests — The tester at 

 each station measures the amfjlification in both directions given 

 by the telephone repeater at that jxiinl and checks the condi- 

 tion f)f the vacuum tubes. 



3. Balance Tests — At each repeater station the degree of h.il.uKc 

 between the line circuit and the balancing network circuit is 

 checked in both directions. Since it is necessary that each 

 section of the circuit be terminated at the opposite end from 

 the station making the balance tests, alternate repeater stations 

 terminate the circuits and the other stations proceed with their 

 balance measurements. The procedure is then reversed. 



' For description of these tests and their application sec article in this issue " Elec- 

 trical Tests and Their .-Xpplications in the Maintenance of Telephone Transmission," 

 by W. H. Harden. 



