580 BELL SYSTEM TECHNICAL JOURNAL 



the power output from each repeater is 1 milliwatt (corresponding 

 roughly to the average power when the program volume is maximum), 

 the non-linear distortion that occurs in the loading causes an increase 

 in the overall transmission loss of the circuit of only 1 db at 8,000 

 cycles, as compared to the loss for negligibly small power. At 1,000 

 cycles, 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 excellence 

 with respect to non-linear distortion. For a 400-cycle line current 

 of 1 milliampere, the ratio of the third harmonic e.m.f. generated in 

 an individual loading coil to the fundamental e.m.f. is equivalent to 

 a loss of 80 db. The current magnitude above assumed corresponds 

 approximately to the maximum repeater output (single-frequency 

 basis) of 1 milliwatt; the average current that flows in the loading 

 coils is very much smaller due to the smaller average repeater output 

 and to line attenuation. In this connection, it is to be noted that the 

 third harmonic voltage varies with the square of the magnitude of 

 the fundamental current, and directly with frequency. The higher 

 harmonics are, of course, much lower in magnitude than the third 

 harmonic. 



