On Theoretical Signal‐to‐Noise Ratios in F‐M Receivers: A Comparison with Amplitude Modulation

Signal‐to‐noise ratios at the output of an f‐m receiver are determined as functions of the input signal‐to‐noise ratio, clipping level, and i‐f and audio filter characteristics when random (fluctuation) noise accompanies the signal to be observed. Both narrow and broad band f‐m are examined. Specific calculations are made for sinusoidal frequency modulation, and it is indicated how data for this simple type of signal may be related to the more complex phenomenon of speech. The concept of the signal‐to‐noise ratio is redefined to describe more accurately the sensing of a signal in noise, since the conventional definition for f‐m proves inadequate and misleading, except for strong carriers. Extensive comparisons are made with a‐m reception employing a half‐wave linear rectifier, and it is found that for moderate and weak (<3 db) signals a‐m requires less input signal power against the same noise background than does f‐m to achieve the same desired output. This is particularly evident for weak signals. Only ...

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