A Carrier System for 8000-Cycle Program Transmission

the beginning of radio the Bell System has supplied the broadcasting industry the needed interconnecting links between broadcasting stations, studios, and other program originating points. For many years these facilities have been provided at audio frequency over loaded cable pairs,6 or over open-wire lines.8 Because present growth of message facilities over main traffic routes is predominantly in broad-band carrier telephone circuits, it has become desirable to adapt these new carrier facilities for the transmission of high-quality program material. The carrier program system to be described operates in conjunction with message circuits and can be used to provide a band width of either 5000 or 8000 cycles. It can be applied to type K multipair cable,9 type L coaxial cable,16 and type J open-wire carrier systems.11 Use of the 8000-cycle band of course requires more complete equalization than the 5000-cycle band, and requires the frequency space normally occupied by three message channels. It is expected that the 5000-cycle band can be accommodated by displacing two message channels. The carrier program system was developed by 1942 but, owing to the war, its first commercial application was not made until early in 1946 on the transcontinental type K route west of Omaha. It is now in use in all sections of the country, particularly the west and south, on type L as well as type K systems and has been successfully tested on type J. In general, a band width of 5000 cycles is used in these applications.