övermodulation

Övermodulation (Swedish for overmodulation) denotes a condition in which the amplitude, frequency deviation, or digital level of a signal exceeds the intended limits of a modulation system, producing distortion and unwanted spectral components. The term is commonly used in radio transmission, audio recording, and broadcasting.

In amplitude modulation (AM) overmodulation occurs when the modulation index exceeds unity (100%). The carrier envelope is driven through zero and can invert, causing clipping of the envelope, waveform distortion and generation of harmonic and intermodulation products. These artifacts increase occupied bandwidth and can cause interference to adjacent channels. In frequency modulation (FM) the concept refers to exceeding authorized frequency deviation or the linear range of the modulator; this can result in spurious emissions and degraded fidelity. In digital audio and PCM systems, övermodulation describes signals that exceed headroom and cause clipping, producing harsh harmonic distortion.

Causes include excessive microphone gain, improper limiter or compressor settings, transmitter misadjustment and input signals that are too large or contain unexpected peaks. Effects include waveform clipping, spectral regrowth, reduced intelligibility, and regulatory non‑compliance.

Prevention and mitigation strategies include careful gain staging, use of automatic gain control, limiters and peak compressors, adherence to prescribed deviation or modulation-index limits, and monitoring with modulation meters and spectrum analyzers. Appropriate filtering and transmitter maintenance also reduce the likelihood and impact of övermodulation.