Frequency modulation for power-line carrier current

FREQUENCY modulation is known to most people today as a system of broadcasting that is remarkably free from the effects of interference and is capable of providing high fidelity reception. These advantages have been realized largely by employing frequencies of 40 megacycles and higher which are well above the present broadcast band. A great amount of effort has been devoted to this field, and therefore, frequency modulation has been well analyzed both in theory
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and experiment.
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However, most of the work has been done with systems using a large deviation ratio which is usually defined as the ratio of the carrier deviation from normal to the highest modulating frequency.