Application to the low frequency case of techniques heretofore used in high frequency ionosphere recorders is described. The beat frequency method of generating wide frequency sweeps is used, covering frequencies from 50 kc to 1,000 kc in a short time without band switching. Advantage is gained by the use of transformers containing ferromagnetic cores in the wide-band transmitter amplifiers, but the antenna system, for practical reasons, is very inefficient. Sample records are shown.
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Blair et al. (1953) studied this question.
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