PRACTICAL APPLICATION OP CARRIER SYSTEMS 



4.1 



telephone system. In this picture it will be noted thai the apparatus 

 is mounted on racks about (> feet high and occupying about one square 

 foot of floor space, which are lined up in rows as space permits. Fig. 2 

 shows a terminal of a later type of carrier telephone equipment which 

 was installed between Harrisburg and Detroit. In this case the ap- 



Fig. 2 



paratus for a complete terminal (4 channels) is mounted on four 

 relay bays as shown. The carrier telegraph equipment shown in 

 Fig. 3 is a typical installation of the latest apparatus. Here rack 

 construction is used although the individual panels are considerably 

 larger than the older telephone equipment. 



Present Development 



As pointed out by Mr. Vail in his original announcement of the 

 successful development of the carrier equipment, carrier systems are 

 economical only for the longer circuits in the plant. The cost ot the 

 terminal equipment is so great that short circuits cannot economically 

 be provided by carrier apparatus. Repeaters, tor amplifying the 

 high frequency currents must also be installed at frequent intervals. 



