Amplitude Modulation

$s(t) = A_c\left[1 + m\cos(2\pi f_m t)\right]\cos(2\pi f_c t)$

$m$ is the modulation index (0–1; above 1 causes distortion). The spectrum contains the carrier at $f_c$ and two sidebands at $f_c \pm f_m$, so bandwidth $= 2f_m$.

Total power: $P_t = P_c\left(1 + \dfrac{m^2}{2}\right)$ — at best only one third of the power carries information. Variants: DSB-SC, SSB (half the bandwidth) and VSB. AM is simple to detect with an envelope detector (diode + RC).