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An FM demodulation algorithm with an undersampling rate

The existing method for sampling a modulated signal is the same as that for a non-modulated message signal. Therefore, the quadrature sampling rate for a modulated signal must be larger than its bandwidth. However, a new algorithm, which can recover completely a DC-free message signal from an FM signal at a sampling rate less than its bandwidth, is presented. The new sampling rate limit is also discussed. The investigation shows that the current sampling theorem does not present an optimal sampling rate for recovering the message signal from an FM signal and further modification of the theorem might be needed.