Frequenzmodulationssignals

Frequency modulation (FM) is a method of transmitting information by varying the instantaneous frequency of a carrier wave in proportion to the amplitude of the modulating signal, while the carrier amplitude remains approximately constant. This places FM in the broader family of angle modulation. A common model uses a carrier of frequency f_c and a modulating signal x(t): s(t) = A_c cos[2π f_c t + 2π k_f ∫ x(τ) dτ], where k_f is the frequency sensitivity. The peak frequency deviation Δf = k_f A_m (with A_m the modulating signal’s peak), and the modulation index is β = Δf / f_m, where f_m is the highest frequency in the modulating signal.

FM is valued for its resilience to amplitude noise and amplitude distortions, improved perceptual audio quality, and better performance in fading channels compared with amplitude modulation. However, it requires a larger transmission bandwidth. A common bandwidth estimate is Carson’s rule: B_T ≈ 2(Δf + f_m). The exact channel usage depends on the chosen FM variant and regulatory standards.

Applications include FM broadcasting, where wideband FM provides high-fidelity audio, and various two-way radio and professional audio systems. Variants include wideband FM (WFM) and narrowband FM (NBFM), used for different trade-offs between audio quality and bandwidth. Demodulation typically employs discriminators or phase-locked loop receivers to recover the original modulating signal. The development of FM is closely associated with Edwin Armstrong, who demonstrated its advantages in the early to mid-20th century and helped establish FM broadcasting in many regions.