TELEPHONE SYSTEM OF THE UNITED STATES 57 



the future, while for international connections, of course, very much 

 longer distances than this will be involved. In the United States 

 considerable study is, therefore, being given to the effects of trans- 

 mission delay and to methods of avoiding difficulties on the very 

 long connections including the development of cable circuits of higher 

 speed. 



The toll cable circuits today include two principal types, one, 

 discussed above, for the longer distances having a transmission speed 

 of about 30,000 kilometers a second, and the other for the shorter 

 distances, transmitting a narrower band of frequencies and having 

 about one-half the transmission velocity. In view of the superior 

 transmission characteristics of the long distance type circuits it is 

 the present practice in the design of new toll cable circuits in the 

 United States to limit the use of the short distance type facilities to 

 circuits about 160 kilometers in length if they are to be used for 

 switched business, and about 280 kilometers in length if used only 

 for terminal business. 



Toll Circuit Equipment 



The apparatus required for the operation of toll circuits has been 

 developed in the form of panels mounted on standard bays of angle 

 iron, thus bringing about a great reduction in the space required 

 compared with earlier forms of mounting. Figure 45 shows a bank of 

 30 four-wire repeaters arranged in groups of three, each group being 

 associated with a phantom and its two side circuits. Figure 46 shows 

 the panels containing complete terminal equipment for two type "C" 

 carrier telephone systems (six circuits) with associated testing appa- 

 ratus. 



The equipment is housed in fire-proof buildings. Figure 47 shows 

 a typical telephone repeater station, this one being located at Prince- 

 ton on the cable route between New York and Philadelphia. This 

 building now contains 1,100 repeaters. Some of the telephone re- 

 peater stations now being built are designed for ultimate capacity 

 with extensions of 10,000 repeaters. 



An interesting feature of the long telephone circuits is the use of 

 1,000-cycle current for signaling rather than the lower frequencies 

 which have been general in the past. This higher frequency has the 

 advantage of being efficiently transmitted by the telephone circuit 

 without change in the amplifying apparatus and hence does not re- 

 quire intermediate ringing apparatus. At the terminals it is rectified 

 and caused to operate relays which actuate the desired signal. 



