THE TYPE PI CARRIER SYSTEM 383 



to serve customers beyond that point from physical voice frequency 

 circuit. 



A carrier Hue termination network is also provided to terminate the 

 end of the carrier line at all frequencies and thus prevent reflections from 

 interfering with the transmission at remote carrier terminals spaced along 

 the line. This network and all of the other line networks are available in 

 the pole or crossarm mounted arrangement shown in Figure 14 and de- 

 scribed in Section 4.5. 



Fig. 26 also gives examples of two types of subscriber distribution 

 beyond the remote carrier terminals. One, wire distribution, is indicated 

 by the voice frequency extensions of Channels 1 and 4 and the other, 

 filter distribution, is shown for Channels 2 and 3. Filter distribution 

 permits the carrier line to be used simultaneously for carrier transmission 

 and voice frequency distribution of the derived voice frec^uency circuit, 

 thus saving the pair of wires required if wire distribution were used. 



7.1 Layout Procedure and Ground Rules 



PI carrier channel laj^outs for a given rural line will be based on the 

 forecast of commercial requirements for that route. The Plant Engineer 

 must determine the number and arrangements of channels which can 

 be applied within the system limits to meet that forecast. The locations 

 of remote terminals are then chosen based on customer locations, channel 

 freciuency arrangements, and the availability of commercial ac power. 

 With the terminal locations fixed, the line losses are determined at ap- 

 propriate frequencies and repeaters are specified as necessary along with 

 any line networks and filters required for the layout. 



The characteristics and limitations of the Pi system lead to certain 

 simplified ground rules which may be used in laying out the carrier chan- 

 nels. Some of these rules are summarized in Fig. 27. The stackable fre- 

 quency arrangement is used for non-repeatered operation, and the design 

 of the carrier channels permits the bare line loss of each individual chan- 

 nel to be 30 db at the top frequency between the central office terminal 

 and the remote terminal. 



Another limit shown in the figure is that the dc loop resistance of the 

 voice frequency extension beyond the remote terminal can not exceed 390 

 ohms (5 miles of 109-steel wire) . The 390-ohm limit is determined by the 

 talking battery supply requirements of the 500-type customer telephone 

 sets when the battery is supplied from the remote PI terminal power 

 supply. The PI carrier system has been designed to operate with the 

 500-type telephone set. The improved dialing, ringing and transmission 

 features of that set wall help to insure satisfactory performance of the 



