. The Bell System technical journal . ioncaused by other factors in the cable circuit. X o UJ o z CO tn UJ a: u> HO u / y i ll L 5 M ILS -2 0 11 ^ ^ F1 ^ 10 30 50 100 200 500 1000 CYCLES PER SECOND 2000 5000 8000 Fig. 8—Effective resistance of 22 milli-henry loading coils used on programtransmission circuits in toll cables. Owing to the low hysteresis loss of the compressed powdered per-malloy material, the non-linear distortion introduced by the loadingis inappreciable within the range of volumes handled by this programsystem. For example, in a 1,000-mile circuit for the condition where 58
. The Bell System technical journal . ioncaused by other factors in the cable circuit. X o UJ o z CO tn UJ a: u> HO u / y i ll L 5 M ILS -2 0 11 ^ ^ F1 ^ 10 30 50 100 200 500 1000 CYCLES PER SECOND 2000 5000 8000 Fig. 8—Effective resistance of 22 milli-henry loading coils used on programtransmission circuits in toll cables. Owing to the low hysteresis loss of the compressed powdered per-malloy material, the non-linear distortion introduced by the loadingis inappreciable within the range of volumes handled by this programsystem. For example, in a 1,000-mile circuit for the condition where 580 BELL SYSTEM TECHNICAL JOURNAL the power output from each repeater is 1 milliwatt (correspondingroughly to the average power when the program volume is maximum),the non-linear distortion that occurs in the loading causes an increasein the overall transmission loss of the circuit of only 1 db at 8,000cycles, as compared to the loss for negligibly small power. At 1,000cycles, the loss increment for the same comparison is .13 db. The. Fig. 9—6-Coil loading case for cable program circuit,^th actual size. harmonic production in the coils is another measure of their excellencewith respect to non-linear distortion. For a 400-cycle line currentof 1 milliampere, the ratio of the third harmonic generated inan individual loading coil to the fundamental is equivalent toa loss of 80 db. The current magnitude above assumed correspondsapproximately to the maximum repeater output (single-frequencybasis) of 1 milliwatt; the average current that flows in the loadingcoils is very much smaller due to the smaller average repeater outputand to line attenuation. In this connection, it is to be noted that thethird harmonic voltage varies with the square of the magnitude ofthe fundamental current, and directly with frequency. The higherharmonics are, of course, much lower in magnitude than the thirdharmonic. LONG DISTANCE CABLE CIRCUIT 581 For the purpose of minimizing crosstalk, the
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