ii<i':F.Gii..iHiTir:s ix loaded tei.i-.puone circuits 579 



(ti) If tlu' rt'tiirn loss of a tiiiitc U-iikIIi of line i^ dcsiri'd (Ictcrmiiic 

 tlic transmission loss of this lentil anil look up tlu- rorn-spoiulinjj 

 value of S^ — S on l"ig. S. Add this amount to the \alue of >S found 

 in paragraph (.M. 



KXAMI'I.IC 



As an example to illustrate the application of these methods let 

 us calculate a return loss at 1,000 cycles for No. l!)-H-174-()3 * side 

 circuits such that 90 per cent, of the circuits may be expected to 

 have a higher value and only 10 per cent, to fail liclow it. The neces- 

 sary data are given in Table II, below. 



(1) //=V0.0O62=+0.01292+0.0O452 = 0.0150. 



Fig. 3 gives 36.5 TV as the corresponding value of Sh- 



(2) At 1,000 cycles 74'= ^^^=0.356. 



^olO 



Fig. 4 gives 8.4 TU as the corresponding value of 5a,. 



(3) Since 90 per cent, of the finished lines are to ha\e return losses 

 greater than S and 10 per cent, less F = 0. 1 and f'ig. o gives —3.7 

 TU as the corresponding value of Sf- 



(4) The transmission loss per mile is 0.274. Since the coils are 

 spaced 0,000 feet apart. Fig. 7 gives 8.7 TU as the value of Sa- This 

 same value would be obtained less directly by calculating the loss 



per loading section, 0.274 X vxs?. =0.311 and using Fig. 6. The latter 

 o2o0 



method is used when the spacing is different from 6,000 feet. 



(5) Using equation (42) 



S = Su + S^-\-Sf-Sa =36.5+8.4-3.7-8.7 = 32.5 TU. 



This will l)e found to agree with the 90 per cent, point on the smooth 

 curve plotted in Fig. 10 which is described below. 



(6) In case it is desired find the return loss of a length of this line 

 having a transmission loss of. for example, 6 TU instead of the return 

 loss of the infinite line. Fig. 8 gives S» — 5 = 0.3 from which 



5„ =32.5+0.3 = 32.8 TU. 



Determin.vtion of Toler-vhle Deviations 



To determine the deviations which correspond to an assigned value 

 of the return loss find values of S^, Sf and Sa as in paragraphs (2), 



•In accordance with the practices of the Bell System, this notation indicates a 

 phantom group of .\o. 19 B. & S. conductors in a cable with loading coils spaced 

 6,000 feet apart, the side circuit coils having 174 millihenrys inductance and the 

 phantom coils 63 millihenrys. 



