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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



ment was met by providing improved loading terminations, which kept the 

 resistance component of the cable impedance fairly close to the nominal 

 impedance over the upper part of the frequency-band transmitted by the 

 voice-frequency repeaters, and which also had satisfactory low reactance. 

 Two different but equally satisfactory terminations^^ were developed, to 

 provide flexibility and economy in the loading layouts. One of these was 

 theoretically based on the mid-section termination previously described. 

 This half-section termination was extended to about an 0.83-fractional 

 section, followed at the open-wire junction by a terminal loading unit having 

 inductance values about .36 of the full-weight loading inductances used in 

 the loading designations. The other new loading termination was theo- 



Table XV 

 Voice-Frequency Loading for Incidental Cables in Non-Loaded Open-Wire 



Lines 



Note: The full-coil inductances in millihenrys are given in the loading designations. The 

 first number applies to the side circuits and the second number to the phantom 

 circuit. 



retically based on the mid-coil termination previously described. It used 

 0.86-fractional coils instead of half coils, and had a 0.36-fractional loading 

 section adjacent to the open-wire side. These new loading terminations were 

 known as ''Fractional coil" or "Fractional section" terminations, depending 

 on whether the fractional coil or the fractional section was the terminal 

 element closest to the open-wire line. At the office ends of loaded entrance 

 cables a mid-section loading termination was frequently used, and the re- 

 peater balancing network-circuits were adjusted to correspond with this 

 situation in the line. 



The H31-18 loading system was standardized in 1928 and is still the 

 standard voice-frequency loading system for incidental cables in open-wire 

 circuits which are not arranged or used for carrier operation. 



Loading Systems Data: General transmission data regarding the loading 

 systems briefly described above are given in Table XV. 



