CONQUEST OF DISTANCE BY WIRE TELEPHONY 367 



about 1.4 miles, intermediate between that of the spacings for standard 

 heavy and medium loading. The coil inductances were chosen to provide a 

 cut-off frequency of about 2300 cycles, which was standard for cable loading 

 for nearly two decades. Heavy loading was also considered, but its ef- 

 ficiency would not have been enough better to justify the extra cost and the 

 extra manufacturing and installation efforts in working to difficult rush 

 schedules. 



Since the loading coils were designed to be in approximate cost-equilib- 

 rium with the cable conductors, those used on the 10-gauge quads were nearly 

 as large as the standard open-wire loading coils, and much larger than those 

 used on 13-gauge quads, which in turn were appreciably larger than those 

 used on the 16-gauge pairs. Also, for cost-equilibrium reasons, the phan- 

 tom loading coils were larger than their associated side circuit coils and were 

 potted with them, with the cross-connections between them made inside the 

 cases at the point where the connections to the stub cables were made. 



The manufacture of the Philadelphia-Washington section of the cable 

 and the loading coils was completed during 1911, and commercial service 

 started on March 22, 1912. A great many manufacturing difficulties were 

 encountered in preventing the cable and coil unbalances from reaching un- 

 acceptable magnitudes, including some difficulties not previously expe- 

 rienced in the Boston-Neponset project which were in part due to the larger 

 sizes of conductors. 



As the associated phantom and side coils were potted in the same case it 

 was possible to obtain some crosstalk advantages by poling the unbalances 

 in one t>^e of coil against those in the other type. In order to maintain 

 schedules, it was sometimes necessary to accept loading apparatus and 

 cable lengths having objectionably high unbalances. In such instances, 

 special arrangements were made for installing these items at points remote 

 from the principal toll centers so that the resulting crosstalk would be sub- 

 stantially attenuated before reaching the telephone subscribers. 



In installing the cable, capacitance unbalance test splices were made at 

 7 points in each loading section, following the procedure used on the Boston- 

 Xeponset cable, but working to more severe limits on residual unbalances. 

 In the over-all tests made prior to commercial service, the crosstalk was 

 found to be within permissible limits, but was in excess of values con- 

 sidered satisfactor}\ In consequence, renewed and successful efforts w^ere 

 made to obtain better crosstalk performance in the next section of the proj- 

 ect, that between Hartford and New Haven. 



The transmission tests on the Philadelphia-Washington cable showed the 

 attenuation to be about 13% better than had been estimated on the coarse- 

 gauge circuits. This was in part due to conservatism in estimating, but 

 mainly due to special manufacturing efforts to dry out the cable so as to 



