146 



BELL SYSTEM TECHNICAL JOURNAL 



the amount of distortion which theory and experience indicate should 

 be expected. Then, final adjustments are made by certain specially 

 provided adjustable parts in accordance with the overall measure- 

 ments. Such overall tests and adjustments are, in general, made 

 daily. 



In setting up these circuits, another important consideration is that 

 each amplifier carry its proper load or, in telephone parlance, each 

 amplifier deliver to its associated line the proper output level. To 

 insure this, diagrams are prepared in advance, showing the desired 

 transmission levels at each repeater, a typical diagram being shown 

 in Fig. 3. In setting up the circuits, the repeater gains are first set 



^ TO LOCAL 

 .BROADCASTING 



STATION MONITOR'S 

 i __ _ AMPLIFIER 



-Sdb LEVEL 



3D LLVLL I 



FROM LOCAiTI 

 CIRCUIT ~-f.l_, 



KEY TO SYMBOLS 

 LONG DISTANCE CIRCUIT [r] FILTER 



LOCAL CIRCUIT 



^ AMPLIFIER 



^ REPEATING COIL 



^ LINE EQUALIZER 



P TRANSMITTING INPUT EQUALIZER 



[|] 600<-J ARTIFICIAL LINE 

 [E] LOCAL EQUALIZER 

 VOLUME INDICATOR 



? 



Fig. 3 — -Typical Circuit Layout and Transmission Level Diagram of Program 

 Network Circuits. 



to values which theory and experience indicate should result in con- 

 ditions as shown in the prescribed transmission level diagram. Test- 

 ing current is then applied to the sending end of the circuit and sensi- 

 tive measuring devices are applied at the output of each repeater. 

 If the results of these measurements do not accord with the trans- 

 mission level diagram, suitable adjustments are then made. 



In building up the large chains which tie together a considerable 

 number of radio transmitters, wire distributing centers are provided 

 at strategic points. Figure 4 shows the circuit layout of the various 

 chains which have been referred to and indicates in a general way how 



