Magnetic Generation of a Group of Harmonics

HE use of non-linear ferromagnetic core coils to generate harmonics started with a simple type of circuit due to Epstein 1 which appeared in 1902. Application of the idea was not made to any great extent until it was elaborated by Joly 2 and by Vallauri 3 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. 437 438 BELL SYSTEM TECHNICAL JOURNAL of perhaps greatest importance were to high power, long-wave radiotelegraph transmitters, where the fundamental input was obtained from an alternator. Other applications of the idea of harmonic production by magnetic means have been made in the power and communication fields. 4 It appears that these circuits were all developed primarily to generate a single harmonic. Comparatively good efficiencies were obtained, values from 60 to 90 per cent being reported for the lower harmonics. The theory of frequency multiplication was investigated by a number of workers, among whom may be mentioned Zenneck 6 and Guillemin.