TYPE-0 CARRIER SYSTEM 



695 



By the use of different group carrier frequencies the several four-channel 

 groups are placed in their various locations. As indicated by Figs. 4 and 

 5, high and low group assignments are used for the two directions of 

 each four-channel system. A repeater is provided for each four-channel 

 system and, except in the case of OA, the high and low frequency groups 

 are "frogged" at each repeater, as in the N system. 



Figure (5 shows a block diagram of a complete system. On this figure, 

 and in general on other figures showing filters, a letter code is assigned 

 to designate the kind of filter, with a subscript letter to indicate the 

 particular system in which the filter is used. The several filter designa- 

 tions and number codes are collected for reference in Table I. Much of 

 the apparent complexity of the system, particularly as regards filters, 

 arises out of the use of a single pair for both directions of transmission. 

 Another complexity is occasioned by the requirement that a complete 

 complement of O systems will not always be provided. For example, 

 OB, OC, and OD systems may be used above an existing C system, or 

 similar systems. 



O 100 - 



"■-TERMINAL 



Fig. 5 — ^Type-0 modulation plan. 



