SHORT-HAUL fAHRIKU TELEGRAPH 



685 



in this frequency-modulation system, a sudden loss of 3 db causes little 

 distortion. The series resistances may serve another purpose besides 

 protecting against short circuits. If one branch has a much greater at- 

 tenuation than the others, the resistance values in series with the shorter 

 branches may be increased so that more energy is directed into the longer 

 branch. 



Emergency Circuits 



If a circuit containing no intermediate branches fails, a regular mes- 

 sage circuit can be patched in to replace it until the trouble is cleared. 

 Fig. 15 shows trunks to be used for making this patch in the case of two- 

 wire circuits. They contain 3 db pads which reduce the signal level to 

 compensate for the change from db transmission level on the regular 

 line to +3 db level on the message circuit. 



The 43A1 system may operate also over a four- wire circuit, which 

 accommodates twelve telegraph channels. A patch to an emergency mes- 

 sage circuit would then be made at the four-wire patch bay. Since the 

 circuit used for telegraph would usually be similar to those used for tele- 

 phone message service, no pads to adjust levels would be required for this 



"W^ 



BRANCHING 

 NETWORKS 



BRANCH 

 — LINES--' 



nm^ 



130 B1 



SUBSCRIBER SETS 



Fig. 14 — Intermediate branch lines. 



BRANCHING 



NETWORK 



BRA^4CH LINES 



AND SUB- 

 SCRIBER SETS 



-9DBM 



MESSAGE CIRCUIT 



Fig. 15 — Emergency circuit. 



