SINGING ON TWO-WIRE CABLE CIRCUITS 



619 



or 20 log P = log 0.9 or log P = - 0.002288 or P = 0.99476 or 

 V = 0.00524. Reading on the normal law distribution for this 

 value changes the 20 db limit as computed above to about 20.03 db, 

 the difference being negligible compared to the usual accuracy of such 

 measurements. 



In general, measurements outside of the limits so determined are 

 probably cases of trouble. However, in the case of active singing 

 points, certain systematic changes in the measured values from the 

 computed values must be allowed for before trouble is proved. 



Example 

 Following is an example of the application of these various methods. 

 Given: The following losses at the critical frequency for various 

 successive repeater sections shown in Fig. 1. 



Repeater Section Loss in Db 



A to B 17 



B to C 17 



C toD 18 



D to E 15 



E to F 15 



F toG 16 



Total 98 



The following gains and return losses at the critical frequency are 

 assumed. The gains give a 9 db overall net loss at the critical fre- 

 quency. 



* This is 40 db nominal apparatus return loss plus 1 db allowance as described 

 above. 



t This is 11 db far-end equipment terminating return loss plus 1 db allowance 

 as described above plus twice the loss from the measuring point to the far-end equip- 

 ment. 



t These are the combinations of the three preceding return losses as the sums of 

 their power ratios. 



** Twice the loss of the near-end equipment is included. 



