Magnetic Generation of a Group of Harmonics* 



By E. PETERSON, J. M. MANLEY and L. R. WRATHALL 



A harmonic generator circuit is described which produces a 

 number of harmonics simultaneously at substantially uniform 

 amplitudes by means of a non-linear coil. Generators of this type 

 have been used for the supply of carrier currents to multi-channel 

 carrier telephone systems, for the synchronization of carrier fre- 

 quencies in radio transmitters, and for frequency comparison and 

 standardization. 



A simple physical picture of the action of the circu t has been 

 derived from an approximate mathematical analysis. - The prin- 

 cipal roles of the non-linear coil may be regarded as fixing the 

 amount of charge, and timing the charge and discharge of a con- 

 denser in series with the resistance load. By suitably propor- 

 tioning the capacity, the load resistance, and the saturation in- 

 ductance of the non-linear coil, the amplitudes of the harmonics 

 may be made to approximate uniformity over a wide frequency 

 range. The sharply peaked current pulse developed by condenser 

 discharge passes through the non-linear coil in its saturated state 

 and so contributes nothing to the eddy current loss in the core. 

 In this way the efficiency of frequency transformation is main- 

 tained at a comparatively high value for the harmonics in a wide 

 frequency band, even with small core structures. The theory has 

 also been adequate in establishing a basis for design, and in evalu- 

 ating the effects of extraneous input components. 



I. Outline of Development 



' I ""HE use of non-linear ferromagnetic core coils to generate har- 

 -'' monies started with a simple type of circuit due to Epstein ^ 

 which appeared in 1902. AppHcation of the idea was not made to any 

 great extent until it was elaborated by Joly ^ and by Vallauri ^ in 1911. 

 The frequency multipliers thus developed were limited to doublers and 

 to triplers, polarization being required for the doubler. In these, as 

 well as in subsequent developments, single and polyphase circuits were 

 used, and various arrangements were adopted for the structure of the 

 magnetic core and for the circuit, by which unwanted components were 

 balanced out of the harmonic output path. Later developments had 

 to do with improvements in detail, and with the generation of higher 

 harmonics in a single stage and in a series of stages. The applications 



* Presented at the Pacific Coast Convention of A. I. E. E., Spokane, Washington, 

 September 2, 1937. Published in Elec. Engg. August 1937. 



437 



