The Bell System Technical Journal 



Vol.XXVIIl April, 1949 No, 2 



A Carrier System for 8000-Cycle Program Transmission 



By R. A. LECONTE, D. B. PENICK. C. W. SCHRAMM, A.J. WIER 



With the raj)id expansion of hroad-band carrier lelc|)hone s_vslems throughout 

 the country, the use of these facilities for program transmission has become 

 desirable. This paper describes a carrier program system capable of trans- 

 mitting a band up to about 8000 cycles wide. 



Introductioni 



T7R0M the beginning of radio the Bell System has supplied the broad- 

 -^ casting 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, or over open-wire lines. Because present growth of message facil- 

 ities over main traffic routes is predominantly in broad-band carrier tele- 

 phone 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,^ type L coaxial 

 cable, and type J open-wire carrier systems.^^ 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 e.xpected 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 19-46 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 s}'stcms and has been successfully 

 tested on type J. In general, a band width of 5000 cycles is used in these 

 applications. 



Objectives 



Existing audio-frequency program circuits may be as long as 7000 miles, 

 may have 100 or more dropj^ing or bridging i)oints, any one of which may 

 occasionally transmit to all of the others, and may be arranged for auto- 

 matic reversal of the direction of transmission by means of a control signal. 



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