CARRIER SYSTEM FOR PROGRAM TRANSMISSION 179 



and feeder circuits along the Atlantic and Pacific coasts. On the assump- 

 tion that these routes may some day be largely in carrier, exhaustive tests 

 were made in 1947 of carrier program transmission applied to type K sys- 

 tems between Omaha and Los Angeles, looping back and forth as required 

 to build up long circuits. Live program material transmitted around a 

 7300-mile loop consisting of 10 carrier links in tandem was judged to be of 

 excellent quality by juries composed of experienced and critical observers. 

 Attenuation and delay characteristics of this circuit relative to the 10D9- 

 cycle point are shown in Fig. 8 and indicate that design objectives are met 

 with enough margin to justify practical operation over about 13 hnks in 

 tandem. Background noise was about 53 decibels below the peak signal. 

 Frequency shift due to differences in carrier frequency at the 20 terminals 

 was less than 2 cycles. The time required for a complete reversal counting 

 from the initial control signal release was 3 seconds. Shorter lengths will, 

 of course, have even better performance. These characteristics, while they 

 do not represent perfection in transmission quality, strike a balance be- 

 tween the various engineering limitations, which makes this system compare 

 favorably with the best facilities previously available. 



Conclusion 



At the end of 1948, three years after the first installation, there were 

 appro.ximately 75,000 miles of carrier program circuits in service, about 70 

 per cent of them established full time. This is a substantial proportion of 

 the total mileage of all grades of program service, which is in the order of 

 175,000 miles. The portions of the main transcontinental routes formerly 

 carried by open-wire lines are now in carrier cables. 



References 

 1 "Use of Public Address System with Telephone Lines," W. H. Martin and A. B. Clark, 

 ,4. /. E. E. Journal, April 1923, pp. 359-366. 



2. "High-Quality Transmission and Reproduction of Speech and Music," W. H. Martin 



and H. Fletcher. A. I. E. E. Journal, March 1924, pp. 230-238. 



3. "Telephone Circuits used as an adjunct to Radio Broadcasing," H. S. Poland and 



A. F. Rose. Electrical Communication, January 1925, pp. 194-202. 



4. "Telephone Circuits for Program Transmission," F. A. Cowan. .4. /. E. E. Trans- 



actions, 1929, pp. 1045-1049. 



5. "Wire Line Systems for National Broadcasting," A. B. Clark. BellSys. Tech. Jour., 



January 1930, pp. 141-149. 



6. "Long Distance Cable Circuit for Program Transmission," A. B. Clark and C. W. 



Green. Bell Sys. Tech. Jour., July 1930, pp. 567-594. 



7. "Auditory Perspective" (A symposium), "Transmission Lines," H. .\. .AlTel, R. W. 



Chesnut and R. H. Mills, Electrical Engineering, January 1934, pp. 9-32, 216-218. 



8. "Wide Band Open-Wire Program System," H. S. Hamilton, Electrical Engineering, 



April 1934, pp. 550-562. 



9. "A Carrier Telephone System for Toll Cables," C.W. Green and E. I. Green. Bell 



Sys. Tech. Jour., January 1938, pp. 80-105. 



10. "Cable Carrier Telephone Terminals," R. W. Chestnut. L. AL Ilgenfritz and A. 



Kenner. Bell Sys. Tech. Jour., January 1938, pp. 106-124. 



11. "A Twelve-Channel Carrier Telephone System for Open-Wire Lines," B. W. Kendall 



and H. A. Ailel. Bdl Sys. Tech. Jour., January 1939, pp. 119-142. 



