580 BELL SYSTEM TECHNICAL JOURNAL 



(3) and (4) above and substitute in formula (42) to find the value of 5//. 

 This with a table or chart of TU and current ratio gives the value of 

 H. Limits can then be imposed on the loading coil inductances and 

 section capacities that will insure that the representative deviation 

 will i^dt exceed the \alue // so found. 



Comparison of Different Types of Circuits 



These formulae are useful in comparing the return losses to be 

 expected in various types of circuits which are built with the same 

 accuracy in the matters of coil inductance and section capacity. In 

 such cases it is merely necessary to calculate the quantity Sy, — SA 

 for each circuit and take the difference. 



E.X AMPLE 



As an example compare the No. 19-H- 174-63 side circuits worked 

 out above with No. 16-H-44-S * circuits at 1,000 cycles. Since the 

 deviations and the fraction F are the same only Sw and Sa need be 

 considered. For the No. l(5-gauge circuit /c = 5560 and the loss in 

 TU per mile is 0.236. From these figures: 



Gauge of Line No. 19 No. 16 



These figures show that the return loss of the No. 16-H-44-S circuits 

 should be higher than that of the No. 19-H-174-63 side circuits and the 

 difference to be expected is 5.4 — ( — 0.3) =5.7 TU. 



When the circuits to be compared have the same cutoff frequenc>' 

 the process of comparison is even simpler since the quantity 5a, is 

 then the same in each case. Sa is determined for each circuit as in 

 paragraj)!) (4) above. The difference betwtiii (lie two \ahics of Sa 

 is the difference between the return losses. 



E.XAMPLE 



As an example compare the No. 19-H-174-63 side circuits with 

 No. 16-H-174-63 side circuits. In this case the cutoff frequencies 

 arc the same so w and Sw are the same. It is then only necessary to 

 compare Sa- The loss per mile of the No. 16-gauge circuit is 0.161 



' This notation indicates a side circuit of No. 16 B. & S. conductors in a ciljlc 

 loaded with 44 millihenry coils spaced 6,000 feet apart. 



