Editing Frequency modulation (section)

===Carson's rule===
{{Main|Carson bandwidth rule}}

A [[rule of thumb]], ''Carson's rule'' states that nearly all (≈98 percent) of the power of a frequency-modulated signal lies within a [[bandwidth (signal processing)|bandwidth]] <math> B_T\, </math> of:

:<math>B_T = 2\left(\Delta f + f_m\right) = 2f_m(h + 1)</math>

where <math>\Delta f\,</math>, as defined above, is the peak deviation of the instantaneous frequency <math>f(t)\,</math> from the center carrier frequency <math>f_c</math>, <math>h</math> is the modulation index which is the ratio of frequency deviation to highest frequency in the modulating signal, and <math>f_m\,</math>is the highest frequency in the modulating signal.
Carson's rule can only be applied to sinusoidal signals. For non-sinusoidal signals:

:<math>B_T = 2(\Delta f + W) = 2W(D + 1)</math>

where W  is the highest frequency in the modulating signal but non-sinusoidal in nature and D is the Deviation ratio which is the ratio of frequency deviation to highest frequency of modulating non-sinusoidal signal.