Classical modulation procedures - Signals, Processes, and Systems - page 247

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Illustration 170: FM-signals with different frequency swings

In the top series the FM signal has a hardly discernible frequency swing and in the bottom series it has a
very large frequency swing. The frequency swing is equivalent to the largest deviation of the instantaneous
frequency of the FM signal from the mid-frequency (here 500 Hz). The double frequency swing does not,
however, give the exact bandwidth of the FM signal because the instantaneous frequency is an imprecise
concept. The greater the frequency swing, the greater the bandwidth of the FM signal.

The source signal is sinusoidal in all cases here and is exactly equivalent to the source signals in
Illustration 171 .