THE TYPE PI CARRIER SYSTEM 385 



In addition to bare line loss, the ground rules make allowance for ap- 

 proximately 3 db of miscellaneous losses in any normal channel layout, 

 including bridging losses of carrier blocking networks and other terminals 

 on the carrier line, insertion losses of high-pass filters, and losses in the 

 autotransformer and junction line filters used at the cable-open-wire 

 junction. Since these losses do not all add directly, it is simpler to use an 

 average loss factor to co\'er most conditions rather than make compu- 

 tations to determine a definite loss for each set of conditions that might 

 exist. Thus for channels using a stackable frequency arrangement, a 

 maximum of about 33 db loss, including the bare line loss and miscel- 

 laneous losses, may be expected between the points where the terminals 

 connect to the line. 



A further loss is experienced because the remote terminals are bridged 

 onto the carrier line. As a result the carrier power transmitted toward 

 the central office terminal is only +0.5 dbm due to a bridging loss of 

 about 3.5 db at that point. Therefore, in the remote-to-central office 

 direction, the minimum power will be —32.5 dbm (0.5 dbm — 33 dbm) 

 at the line terminals of the central office terminal. The minimum carrier 

 power in the central office to remote direction will be —29 dbm (+4 

 dbm — 33 dbm) at the bridging point of the remote terminal. 



7.2 Terrninal and Repeater Location 



In laying out the carrier line design, it is ffi"st necessary to determine 

 the possible locations for the remote terminals based on distances to 

 the customers to be served and the a\'ailability of conmiercial ac power, 

 since this is the most economical power source. (When commercial ac 

 power can not readily be made available, the primary air cell batteries 

 can be used.) Having determined the ideal location of the terminals from 

 a physical standpoint, the makeup of the physical circuits back to the 

 central office must be determined and computations made of the carrier 

 frecjuency attenuation of the facilities. These loss computations are used 

 to determine the number of repeaters required, if any, and their locations, 

 once again modified by availability of commercial power. The Plant 

 Engineer must also check for the necessity of input and output pads at 

 the terminals and repeaters. 



The need for loss computations led to the development of length-loss 

 charts so that a carrier line design could be made in a manner ^•ery similar 

 to the loop cable design using the Resistance Design JNIethods as men- 

 tioned earlier.* Fig. 28 shows one of the 96-kc length-loss charts used 

 to lay out repeater spacings and Channel 4 over-all circuit design. Fig. 29 

 shows the 48-kc length-loss charts as an example of the charts that are 

 provided at each carrier frequency other than 96 kc for terminal-to- 



