rarchy (U.K.) Five groups are translated using carriers spaced 48kHz apart to set of channels and identifies it in the higher order band of frequen- form a 'supergroup' in the range 312kHz to 552kHz. A supergroup cies. contains 60 channels. Groups and supergroups are used to construct systems on open Where a suffix has been added i.e. group 5 or supergroup 12, the wire and symmetrical cable. The line frequency spectrum of the suffix refers to the carrier that will be used to translate that particular typical systems are shown in Figure 20.3. CH11CH12 96 100 104 108 112 116 120 124 128 132 136 140 B-A Direction A-B Direction Line Frequency kHz SOJ-A Pilots Supergroup 1 Supergroup 2 Line Frequency kHz Figure 20.3 Typical open wire and symmetrical pair systems: (a) open wire, 12 channel; (b) symmetric pair, 120 channel Frequency translation 20/5 20.3.4 Higher order translation alternative scheme for building large systems, which avoids the large 15 supergroup blocks but introduces more stage of translation. Above supergroup level different administrations have adopted Three mastergroups, mastergroup 7, 8 and 9, are translated to a different hierarchies to build large systems. Three schemes have supermastergroup 8516kHz to 12338kHz and supermastergroups been identified and are described below: are used in further translations stages for 12MHz, 18MHz, and 1. The 15 supergroup assemblies (UK). 60MHz systems. 2. The mastergroup and supermastergroup assemblies (Europe). 3. The Bell mastergroup plan (USA). 20.3.4.3 Bell system 20.3.4.1 15 supergroup assemblies The Bell system (Figure 20.6) has adopted a different mastergroup arrangement in that 10 supergroups are required to form a master- Supergroups 2 to 16 (Figure 20.2) are translated to the band 312 to group. The supergroup carrier frequencies vary according to the 4028kHz and form the 15 supergroup assembly or 'hypergroup'. system usage resulting in different mastergroup frequency alloca- Note that supergroup 2 is not translated and passed forward directly tions. The