Negative Impedance Telephone Repeaters

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 repeater 1 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 overall 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 1055 1086 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 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. In the period from 1948 to the present time, over 50,000 series-type negative impedance repeaters were manufactured and incorporated in the Bell System telephone plant. These repeaters have been used largely on intraexchange trunks and on trunks extending from the exchange areas to near-by smaller towns. Such installations have been very effective in improving the transmission 011 short haul calls and in many cases have also reduced trunk costs by permitting the use of smaller and cheaper conductors. They are usually operated at gains that reduce the nonrepeatered trunk loss by more than half.