TELEPHONE TRANSMISSION OVER LONG CABLE CIRCUITS 7? 



he receives, while the curve for the "talker" is referred to the power 

 which he puts into the circuit. 



In Figure 4 showing the condition existing in a two-wire circuit, 

 the comparative magnitudes of the power in each echo are indicated, 

 a typical condition of the lines being assumed. For the listener the 

 echo power is expressed as a percentage of the directly transmitted 

 power which he receives. In the case of the talker, it is expressed 

 as a percentage of the power which he puts into the circuit. In 

 addition to the comparative amounts of power in each echo, "weight- 

 ed" magnitudes are indicated. The "weighted" figures take account 

 of the fact that the effects of a given amount of echo become more 

 serious as the time lag is increased as indicated by the curves in Figure 



■S"P- 



Time in Seconds 

 Fig. 5 — Effect of echoes on talker and listener. 



5. Referring to Figure 4, it will be noted that the "weighted" mag- 

 nitudes of the power in the echoes are largest for the long paths. In 

 general, this condition exists in the case of the majority of long two- 

 wire repeatered circuits in cable. 



In order to compare the behavior of a four-wire circuit with a two- 

 wire circuit, consider again Figures 3 and 4. It will be observed that 

 in Figure 4, showing the two-wire circuit, there is one echo received 

 by the talker which travels from one end of the circuit to the other. 

 Referring to Figure 3 showing a four-wire circuit, it will be seen that 



