SINGING ON TWO-WIRE CABLE CIRCUITS 



609 



The other important point in determining the singing point dis- 

 tribution is to fix the amount by which its average is less than say, 

 the reference 63 per cent point on the Sf curve; i.e., if the distribution 



99.8 



99.S 



• 99 



98 



0.5 



0.2 



0.1 



0.05 



-2 2 



DEVIATION IN DECIBELS 



Fig. 6 — Distribution functions for return losses and singing points. 



curve of single frequency return losses for, say, the highest frequency 

 having as much gain in the repeater as the gain at 1000 cycles, is 

 •Si + Sf, the distribution of singing points will h& S\ — B ■\- Sq (2.0) 

 where B is S\ minus the average of the singing points, Sq (2.0) is a 

 normal law with a standard deviation of 2 db, and Q is the percentage 



