Negative-impedance telephone repeaters ¿ Application in the Bell System

THE application of the telephone repeater, the development of which made countrywide telephone service practicable, had been confined largely to toll plant from the year 1915 when the transcontinental line was first established, until a few years ago. About 1948 the negative-impedance repeater1 was developed and placed in production. This repeater operates on the principle of inserting negative resistance (and, if desired, negative inductance or capacitance) in series with the line, thus reducing the over-all impedance and increasing the current in the line. This results in transmission gain in the same sense as that resulting from a repeater of the conventional type. This principle and the package nature of the assembly resulted in a telephone repeater so low in cost and so simple in application and installation that it has found extensive use primarily in the local telephone plant.