760 



THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1951 



length about 5} inches. The container dimensions are such that the small 

 energy losses in the container-material have unobjectionable reactions upon 

 the frequency-resistance and inductance characteristics of the coils. 



A comparison of the effective resistance characteristics of representative 

 toroidal and solenoidal types of carrier loading coils is of interest at this 

 point. 



Referring to table XVIII, the more favorable resistance values of the 

 solenoidal coils at 30 kc. and above are due to greater refinements in the 

 stranding of the copper conductors. The relatively small coil size, however, 

 penalizes the low-frequency resistance; this is tolerable in the Type J 

 systems because of the relative unimportance of the voice-frequency circuit. 



Terminal Loading Units: For engineering flexibility in the loading layouts, 

 and to minimize the cost of building out the terminal loading sections, two 

 different, equally satisfactory, types of compensated loading terminations'*' 

 are provided for use with Type J carrier loading systems. One of these is 

 electrically analogous to that used with the 30-kc. and 10-kc. loading sys- 

 tems, and is theoretically based on the half-coil termination previously 

 described. Lower inductance and capacitance elements are used because of 

 the much wider carrier frequency-band. The alternative type of loading 

 termination is theoretically based on half-section termination. It involves an 

 extension of the terminal loading section from half-section to about 0.8 full- 

 section and the use of a terminal loading unit which employs a fractional 

 weight loading coil (approx. 0.32 full-coil inductance) in series with the 

 cable, and which has equal-capacitance condensers connected in parallel 

 across each of the two line windings of the fractional coil. 



Table XVIII 

 Effective Resistance Data — Representative Carrier Loading Coils 



At the junctions of cable and open wire, the cases which pot the shielded 

 terminal units in pairs are mounted on crossarm fixtures in close proximity 

 to the bare open wire. In office installations, the loading unit assemblies are 

 mounted on individual panels for installation on an equipment bay in close 

 proximity to the associated Type J system line filters. 



Building-Out Units: The building-out apparatus used in conjunction with 



