 economic factors, these trunks used VF (analog wire-pair) transmission over cable. In North America, this type of transmission is phasing out in favor of a digital connectivity. However, analog wire-pair transmission still persists in a number of parts of the world, especially outside of North America. In the United Kingdom the term junction is used for trunks serving the local area, whether analog or digital. There are notably less trunks than subscriber lines for which they serve. This is due to the concentration at a local serving switch. The ratio of trunks to subscriber lines varies from 3 to 25. Because there are less trunks, more investment can be made on this portion of the plant. Losses are generally kept around 2 dB and return losses are well over 24 dB because of excellent impedance matches. These low trunk insertion losses can accomplished by several means such as using larger-diameter wire pairs, employing VF amplifiers and inductive loading. 5.5.2 Inductive Loading of Wire-Pair Trunks (Junctions) The approach to inductive loading of wire-pair trunks is similar to that for loading sub- scriber loops. The distance (D) between load coils is all important. The spacing (D) should not vary more than +2 from the specified spacing. The first load coil is spaced D/2 from an exchange main frame, 8 where D is the specified distance between load coils (see Table 5.3). Take the case of H loading, for instance. The distance between load coil points is 6000 ft (1830 m), but the first load coil is placed at D/2 or 3000 ft (915 m) from the exchange. Then if the exchange is bypassed by some of the pairs, a full-load section exists. This concept is illustrated in Figure 5.5. Now consider this example. A loaded 500-pair VF trunk cable extends across town. A new switching center is to be installed along the route where 50 pairs are to be dropped and 50 inserted. It would be desirable to establish the new switch midway between load points. At the switch, 450 circuits will bypass the office (switch). Using this D/2 techn