450 



THE BELL SYSTEM TECHNICAL JOURNAL, APRIL 1951 



mf/mi 19 and 16-gauge cables, Codes TB and TH, respectively, for which 

 the early loading standards had been originally estabUshed. 



With respect to the use of loading the most important of the new cables, 

 above referred to, were: (a) a 455-pair,(^) 19 ga. cable, Code BNB, having 

 a mutual capacitance of about 0.085 mf/mi, and (b) a 909-pair,(^> 22 ga. 

 cable. Code SA, having a mutual capacitance of about 0.083 mf/mi. Also 

 there was a 1212-pair 24 ga. cable having a mutual capacitance of about 

 0.079 mf/mi. Fractional-size cables having these properties became avail- 

 able subsequently. The 24 ga. cable did not become an important field for 

 the economical use of loading until the late 1920's, following the develop- 



^'> In the tabulated data, the capacitance of 19BNB and 22SA cables are assumed 

 to be 0.085 and 0.083 mf/mi, respectively, and their resistance 85 and 170 ohms per 

 loop mile at 68° F, 



<2) The first word in the compound designations appHes to the coil inductance ("Medi- 

 um" = .175 mh; and "Light" =0.135 mh). The second word in the compound desig- 

 nation applies to the coil spacing ("Heavy" = 1.14 mi; and "Medium" = 1.66 mi). 



ment of the low-cost, compressed, permalloy-powder core loading coils de- 

 scribed in Section 19. 



16.2 New Loading Arrangements 



In order to avoid an objectionable degradation in transmission service, 

 new loading systems were standardized during 1922 for use on the high- 

 capacitance 19 ga. and 22 ga. cables, above mentioned. These involved the 

 use of the standard medium loading coil (Code 574, inductance 175 mh) 

 at "heavy" spacing, and of the standard Hght loading coil (Code 575, in- 

 ductance 135 mh) at ''medium" loading spacing. Initially, these new load- 

 ing systems were known as "medium-heavy" and "Ught-medium" loading. 



Co) The largest number of pairs previously available in 19 and 22 ga. cables were 303 

 and 606, respectively. 



