Frequency Modulation

FM varies the carrier's frequency, giving better noise immunity at the cost of more bandwidth.

Intermediate

The instantaneous frequency is $f_c + k_f\, m(t)$ . The modulation index is $\beta = \Delta f / f_m$ .

Carson's rule estimates bandwidth:

$B \approx 2(\Delta f + f_m)$

FM broadcast radio uses $\Delta f$ = 75 kHz and $f_m$ up to 15 kHz → about 180 kHz, within its 200 kHz channels. FM's constant amplitude makes it robust against amplitude noise and suits efficient non-linear power amplifiers.

Spotted a mistake or want to add detail? Suggest an improvement — Content Contributors' edits are reviewed by editors before they go live.

Discussion (0)