The ON/K carrier system

Due to the recent growth of telephone requirements in northern California, a constant search is being made for better methods of using the basic telephone facilities in this area. One of the facilities which was looked at was the cable pairs used by the K carrier systems. This system, by design, is a long-haul carrier. That is, it is designed to provide circuits that have transmission characteristics suitable for 4,000-mile circuits. However, since the capacity of this system is only 12 circuits it was seen to be advantageous to devise some method to increase the capacity of the cable pairs. The circuits derived by such an addition could be short-haul, of 100 to 200 miles. The requirements for new long-haul circuits are being filled by the L1, L3, TD2, and in the future, TH carrier systems. The objective then of examining the K carrier cable pairs was to provide a method of deriving additional short-haul voice channels on these same pairs. One of the stipulations for any method of accomplishing this, however, is that no degradation of the K carrier systems should result from the modification or addition. A second stipulation, since the need for the additional channels was fairly urgent, is that any instrumentality employed should use as much existing equipment as possible in order to minimize the development time. With these factors in mind, a study was started which eventually led to the development of the ON/K system. This paper describes the development and the use of these systems in the northern California area of the Pacific Telephone Company.