FM - CW (frequency modulated continuous wave) radar
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Indirect method of level measurement
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Requires Fast Fourier Transform (FFT) analysis to convert signals into a frequency spectrum
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FFT analysis requires processing power and therefore practical FM - CW process radars have to be four wire and not two wire loop powered
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FM - CW radars are challenged by large numbers of multiple echoes (caused by the parabolic effects of horizontal cylindrical or dished topped vessels)