MAGNETIC GENERATION OF A GROUP OF HARMONICS 445 



coil is worked in the saturated state where its inductance Lis is low. 

 Since the resistance of the winding is small, the potential drop across 

 the coil is correspondingly small. The current i^ which charges the 

 condenser C2, assuming the latter to have zero charge at the start, is 

 therefore negligible as indicated in Fig. 6c. This state of affairs is 

 maintained until the current through L2 reaches the value — /q, at 

 time tc. At this point the inductance of the coil increases suddenly to 

 L20 and the voltage across the coil tends to increase. Hence the 

 current i^ increases and C2 is charged much more rapidly than in the 

 preceding interval. Charging continues until the current through the 

 coil increases through /o at time td- At that time, the coil inductance 

 returns to the low saturation value L^s, and the potential across the coil 

 decreases. The condenser potential is no longer opposed by the poten- 

 tial drop across the coil and the condenser discharges through R2 and 

 Lis ; ii reverses its direction, maintaining the coil in the saturated region. 

 The form and duration of the sharply peaked discharge pulse charac- 

 teristic of this type of harmonic generator are determined by the values 

 of the elements just mentioned. The resistance, capacity, and satura- 

 tion inductance effectively in circuit are adjusted to permit the current 

 to rise to a high maximum, to damp the pulse, and to shorten the pulse 

 duration to the point at which the highest harmonic required reaches 

 the desired amplitude. Under the working conditions which will be 

 assumed in the following, this insures that the pulse dies away before 

 the end of the half-cycle as shown in Fig. 6c. At that time the currents 

 and potentials are the same, except for reversals of sign, as those at the 

 start, so that the current wave consists of an alternating succession of 

 these pulses. Equivalent circuits for the three respective time inter- 

 vals of a half-cycle are shown in Figs. 6d, 6e, 6/. The similarity of the 

 load current wave form derived above to that experimentally observed 

 and shown in Fig. 2, is to be noted. 



The course of events described above parallels closely conclusions 

 drawn from the mathematical analysis. This picture attributes to the 

 coil L2 a sort of switching property which permits the condenser C2 in 

 the load circuit to be charged and discharged alternately. The charge 

 starts when the large inductance L20 is switched across the primary and 

 secondary meshes, thus permitting energy to flow from the primary 

 circuit into the condenser C2. This corresponds to that part of the 

 wave described above during which the load current slowly rises as the 

 charge accumulates on C2. Discharge starts when the large inductance 

 L20 is switched out and the much smaller inductance Lis is switched in. 

 This sharply reduces the voltage across L2, and the condenser is dis- 

 charged through the load resistance and the saturation inductance. 



