LONG DISTANCE TELEPHONE CIRCUITS 521 



Haven, a distance of 79 miles (127 kilometers), and between New 

 York and Philadelphia, a distance of 87 miles (140 kilometers). 

 These 1906 cables contained No. 14 A. W. G. conductors (1.6 milli- 

 meters in diameter) and were loaded with 250-millihenry inductance 

 coils spaced about 6CG0 feet (1830 meters) apart. By means of these 

 cables it was possible to obtain transmission equivalents low enough so 

 that these circuits furnished what was then considered very good long 

 distance service. These early cables consisted entirely of physical 

 circuits. 



In order to obtain more circuits from the same number of wires, 

 much development effort was then spent on methods for phantoming 

 cable circuits and loading the phantoms. A number of problems 

 were encountered and solved, the most serious being the problem of 

 avoiding undue crosstalk between the circuits due to fortuitous 

 unbalances introduced at the loading points and between the cable 

 conductors. The problem was finally solved and in 1910 a short 

 cable was installed between Boston and Neponset, Mass., providing 

 loaded phantom circuits as well as side circuits, thus increasing the 

 number of circuits 50 per cent. This was followed by a rapid extension 

 of the use of this type of cable. 



The ultimate in large gauge loaded cables was achieved in 1914 

 when the installation was completed of underground cable from Boston 

 to Washington, a distance of 450 miles (724 kilometers). New York 

 City being about at the midpoint. Some of the conductors in the 

 cables were No. 10 A. W. G. (2.6 millimeters in diameter) while others 

 were No. 13 A. W. G. (1.8 millimeters in diameter). Most of the load- 

 ing consisted of 200-millihenry coils on the sides and 135-millihenry coils 

 on the phantoms, spaced 7400 feet (2255 meters) apart. The 1000-cycle 

 losses per mile (per kilometer) on these circuits were .050 (.031) db for 

 the sides and .040 (.025) db for the phantoms for No. 10 A. W. G. and 

 .085 (.053) db and .070 (.043) db for the side and phantom, respectively, ' 

 of No. 13A. W. G. 



The vacuum tube telephone repeater was demonstrated as a great 

 success when the New York-San Francisco telephone line was officially 

 opened January 25, 1915. When this device was applied to the then 

 available loaded cable circuits various imperfections, unimportant on 

 non-repeatered circuits, produced serious effects, some of which had 

 already been encountered in the work leading up to the loading of the 

 open wire transcontinental line. Among these were the impedance 

 characteristics of the cable circuits which were irregular due in part 

 to insufficient stability and uniformity in the capacitances of the 

 individual loading sections. These impedance irregularities prevented 



