TWELVE-CHANNEL OPEN-WIRE CARRIER SYSTEM 371 



suitable for J system operation. The left-hand diagram shows a 

 method of reconstructing part of one of the older types of open-wire 

 lines built with 12-inch spacing between wires of the pairs and with the 

 "Alternate Arm" transposition system which was developed for the 

 use of type C systems on the side circuits of the horizontal phantom 

 groups on alternate arms. This method is a flexible one in that one or 

 more phantom groups may be converted at a time, as on the second 

 crossarm shown. For such an application not only was removal of the 

 phantoms and retransposition necessary, but the spacing of the two 

 wires of each pair was reduced to 6 inches. This general method of 

 construction was used for the Dallas-Houston and Dallas-San Antonio 

 lines,® except that the 6-inch pairs were constructed with new wire on 

 a new crossarm rather than by respacing 12-inch pairs. 



Another common type of open-wire pole head configuration, the 

 middle diagram of Fig. 5, is that made up of 8-inch spaced non- 

 phantomed pairs transposed in accordance with the K-8 transposition 

 system on an eight-span base. Through design studies supplemented 

 with field experiments it was found that such a line could be converted 

 for J systems much more cheaply than an Alternate Arm line. If J 

 systems are restricted to the pairs on the outer ends of the crossarms, 

 with two inner pairs, about one or two transposition changes in each 

 pair per mile are enough. This scheme was followed in reconstructing 

 the line between Charlotte, North Carolina, and West Palm Beach, 

 Florida. 



For new lines yet to be built, a greater degree of latitude in structural 

 design is naturally possible. The right-hand diagram of Fig. 5 

 shows an open-wire pole head configuration designed to allow J 

 systems to be operated on all of the pairs. The unique feature of this 

 configuration is that, while 8-inch spacing is preserved between the 

 wires of the various pairs, the adjacent non-pole pairs on a crossarm are 

 separated by twenty-six inches and the crossarms by thirty-six inches. 

 The reduction in coupling made possible by this increased spacing 

 keeps the crosstalk for any combination of pairs down to a suitable 

 value with transposition arrangements not necessarily more compli- 

 cated than those employed for the other configurations. This type of 

 construction was used for the new parts of the Fourth Transcontinental 

 line. 



Fig. 6 shows a comparison of the number of transpositions 

 used in a typical section of open-wire line for various types of circuits 

 from voice frequency phantomed circuits to non-phantomed circuits 

 intended for J system operation. From the original arrangement 

 where there was one transposition point in every ten spans, about 



