TWO-TERMINAL BALANCING NETWORKS 



289 



determines R3 as 2100 ohms and R2 is then automatically determined as the 

 difiference between the i?-intercept of the Rs semicircle and Ri , hence R2 

 = 420 — 130 = 290 ohms. To determine C3 , choose the A'cj semicircle at 500 

 cycles to intersect the R-i semicircle at a point near the 500-cycle impedance 

 of the cable impedance function, but make some allowance for the added 

 negative reactance of the R1C2 generating function. The determination of 

 C2 can be made in either of two ways. First an Xr. semicircle can be drawn 

 at 5000 cycles which intersects the R-2 semicircle at an impedance near the 

 5000-cycle impedance of the cable. The imj)edance at 1000 cycles can then 

 be found graphically for R2C2 and R3C3 and added together to Ri . This 



800 1000 



RESISTANCE 



Fig. 5 — Graphical design of two-terminal balancing network for 19-ga. quadded 

 non-loaded toll cable. 



total impedance at 1000 cycles should provide a good simulation of the 1000- 

 cycle impedance of the cable. A second procedure for finding C2 would be 

 to follow a somewhat reverse process: Determine the 1000 cycle Z for the 

 Rad function and subtract it from the 1000 cycle Z of the cable. Choose Ci 

 such that the intersection of the R^Co semicircles is near the point deter- 

 mined by the subtraction of R^Cz from the cable. 



To avoid confusion of lines the construction circles have been omitted 

 from this last drawing except to show the addition of the lOOO-cycle im- 

 pedances. As may be seen this network shown in Fig. 5 provides a rather 

 good simulation throughout the frequency range above 200 cycles. 



