lOGO THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



the trunks has been assumed. In considering this chart it will be seen 

 that non-loaded 24-gaiige conductors can be utilized for the shorter 

 distances up to about two miles. The next step is to apply loading, which 

 is indicated in the chart by the symbol H88 meaning 88 millihenry coils 

 at 6,000 foot spacing. After reaching the limit of about 7 miles without 

 repeaters on 22-gauge, the differential between 22- and 24-gauge is 

 more than enough to pay for a repeater, the simple series repeater (E2) 

 being used for distances up to 10 miles and then the improved E23 re- 

 peater extending the use of 24-gauge to about 14 miles. Beyond this 

 point the most economical combination is indicated. 



The general effect of the introduction of the negative impedance re- 

 peater is to shift the average gauge distribution so that more small gauge 

 cable can be economically utilized, accompanied in most cases by im- 

 proved transmission. It will be noted from the figure that no 19-gauge 

 cable will need to be added in the future to care for interoffice trunks 

 up to distances as great as 25 miles between offices. Of course, in cases 

 where 19-gauge is already available in plant it can be used to advantage 

 despite the fact that for new construction a smaller gauge with the nega- 

 tive impedance repeaters would be cheaper. 



It has also been assumed in making up Fig. 1 that supervision or 

 pulsing requirements will not limit the use of the smaller gauges. In a 

 specific case where some of the older type central offices are involved, 

 signaling may have an important bearing and substantially distort the 

 economic ranges indicated on the chart. 



Fig. 2 illustrates the field of use of toll connecting or tandem trunks. 

 As a toll connecting trunk forms part of a multilink connection, and 

 since there are always at least two (and often more) trunks in series on 

 connections involving these trunks, the Bell System companies find it 

 economical to plan for a maximum loss of 3 db for this type of trunk. 

 Likewise for the tandem trunks, where two in series may be used in 

 place of an interoffice trunk, 3 db is considered a reasonable ol:)jective. 



It will be noted again by referring to this chart that 19-gauge has very 

 little future field of use and in all cases the new "series-shunt" repeater 

 will be utilized rather than the earlier series type because of return loss 

 considerations and also because of the greater gain required to reduce 

 the trunk losses to the desired values. In the tandem and toll connecting 

 case, signaling may again be a distorting factor though not to so great 

 an extent as in the direct interoffice trunk case. To this extent, however, 

 the curves are theoretical, as they haxe been made up without regard 

 to this limitation which may apply in a few practical cases. 



