764 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



side circuits, the average geographical spacing for the full-weight phantom 

 loading units ranges from about one mile to nearly 6000 feet. 



The voice-frequency attenuation in the loaded phantom circuits is ap- 

 preciably lower than that in the associated side circuits. The small trans- 

 mission impairments which the phantom loading apparatus introduces into 

 the associated carrier side circuits are negligible. The voice-frequency 

 impedance-matches between the loaded cable phantoms and the (non- 

 loaded) open-wire phantoms are nearly as good as those obtained with 

 voice- frequency phantom group loading. 



An interesting feature of the phantom loading under discussion is that it 

 uses a 2-coil scheme, with similar phantom coils in each side circuit at each 

 phantom loading point. This scheme is one of several covered by the basic 

 phantom loading patent {U. S. No. 980,921; Jan 10, 1911) but was not 

 used commercially in the Bell System until the late 1920's when very severe 

 side-to-side crosstalk limits became necessary in phantom-group carrier 

 installations for the control of high-frequency intersystem crosstalk. This 

 control was strengthened by shielding the two associated phantom loading 

 coils from one another. 



Bibliography {Continued) 



6. B. Gherardi, "Commercial Loading of Telephone Circuits in the Bell System," Trans. 



A.I.E.E., Vol. XXX, p. 1743, 1911. 

 8. Thomas Shaw and William Fondiller, "Development and Application of Loading for 

 Telephone Circuits," Trans. A.I.E.E., Vol. XLV; Published in The Bell System 

 Technical Journal, Vol. V, pp. 221-281, April 1926. 



12. R. S. Hoyt, "Impedance of Loaded Lines and Design of Simulating and Compensating 

 Networks," B.S.T.J., July 1924. 



26. V. E. Legg and F. J. Given, "Compressed Powdered Molybdenum-Permalloy for 

 High-QuaUty Inductance Coils," B.S.T.J., Vol. XIX, p. 385, 1940. 



30. S. G. Hale, A. L. Quinlan and J. E. Ranges, "Recent Improvements in Loading Ap- 

 paratus for Telephone Cables," Trans. A.I.E.E., Vol. 67, 1948. 



36. E. H. Colpitts and O. B. Blackwell, "Carrier Current Telephony and Telegraphy," 



Trans. A.I.E.E., Vol. XL, p. 205, 1921. 



37. H. A. Affel, C. S. Demarest and C. W. Green, "Carrier Systems on Long Distance 



Lines," Trans. A.I.E.E., Vol. 48, 1928; B.S.T.J., Vol. VII, July 1928. 



38. J. T. O'Leary, E. C. Blessing and J. W. Beyer, "A New Three-Channel Carrier Tele- 



phone System," B.S.T.J., Vol. XVIII, Jan. 1939. 



39. H. S. Black, M. L. Almquist and L. M. Ilgenfritz, "Carrier Telephone System for 



Short Toll Circuits," Trans. A.I.E.E., Vol. 48, 1929. 



40. H. J. Fisher, M. L. Almquist and R. H. Mills, "A New Single Channel Carrier Tele- 



phone System," Trans. A I E.E., Jan. 1938; B.S.T.J., Jan. 1938. 



41. B. W. Kendall and H. A. AfTel, "A Twelve Channel Carrier Telephone System for 



Open-Wire Lines," B.S.T.J., Vol. XVIII, Jan. 1939. 



{to be concluded) 



