A new 4-channel open-wire carrier system employing transistors

AMONG independent telephone companies, Bell System operating companies, and railroad communications systems, carrier is used to exploit fully the vast mileage of open-wire telephone plant. Consistent with circuit needs, wire lines were first used to transmit voice-frequency circuits and, later, with added transpositions, to transmit carrier circuits employing frequencies to about 35 kc. Even now, after more than 30 years of such growth, however, the great majority of open-wire message traffic for short- and medium-haul distances is transmitted at carrier frequencies below 35 kc. The number of circuit miles in these carrier frequencies is now in the millions. Continued major growth is expected in open-wire plant, not by adding more wire lines but by moving to higher frequencies.