234 BELL SYSTEM TECHNICAL JOURNAL 



loading systems having a nominal impedance approximately 60 per 

 cent, as high as their associated side circuit loading systems. The 

 transmission efficiency of the phantom circuit was 20 to 25 per cent, 

 better than that of its associated side circuits, on which basis, the 

 phantom circuits were suitable for use over somewhat longer distances 

 than their side circuits. 



Cable Loading. Data regarding the general characteristics of the 

 first phantom group loading systems standardized for use on quadded 

 telephone cables are given in the first four rows of Table \'. These 

 loading systems were used principally on interurban toll cables. 

 Because of the extra cost of the terminal and signaling equipment, 

 and other factors involved in phantom working, it was not economical 

 to use phantom circuits in the shorter lengths of loaded cable ordi- 

 narily involved in exchange area connections. 



As soon as the development work on quadded toll cables and 

 phantom group loading had progressed to a point where satisfactory 

 commercial results were assured, active development work com- 

 menced on the Boston-New York-Washington cable project, invoK ing 

 the use of coarse gage quadded conductors and new types of high 

 efficiency loading coils designed especially for use on the coarse gage 

 wires. The Boston-Washington cable was the first link in a rapidly 

 growing network of toll cables which now interconnects the large 

 population centers of the Atlantic Seaboard and the upper Mississippi 

 V^alley region, providing increased reliability of service as compared 

 with open wire lines. 



It should be kept in mind that at the time under discussion (1910- 

 1911) no commercially satisfactory type of telephone repeater was 

 available. Accordingly, in order to assure satisfactory service be- 

 tween Boston, New York, Washington, and intermediate points, 

 it was necessary to provide 10-A.w.g. and 13-A.w.g. conductors in the 

 new cable. Cost studies showed it to be desirable to use a special 

 weight of loading intermediate between the old heavy and medium 

 loading systems, which was therefore designated "Medium-heavy" 

 loading. Information regarding this special loading is given in Items 

 1 and 2 of Tal)le W In items 3 and 4, corresponding data are gi\-en 

 on the "high-efficiency" heaxy loading designed for coarse gage 

 conductors. This heavy loading was used on certain sections of the 

 Boston-Washington cable where plant construction reasons made it 

 desirable to install the coils in existing loading manholes installed at 

 heavy loading spacing. 



From the last column of Table \' il is seen thai ihere is \ery little 

 difference between the efficiencies of the hea\\" and the medium- 



