modulaatioprosentti

Modulaatioprosentti, often translated as depth of modulation, is a parameter used in signal processing and radio engineering to describe how strongly a carrier signal is modulated by an information signal. It expresses the extent of variation in the carrier’s amplitude (or, in some contexts, other properties) caused by the modulating signal. In practice it indicates how much the envelope of the modulated wave fluctuates due to the information content.

For a carrier with peak amplitude Ac and a sinusoidal modulating signal with peak amplitude Am, the modulation index m is defined as m = Am / Ac, and the modulation percentage is M% = m × 100%. If the modulated envelope varies between a maximum amplitude Amax and a minimum amplitude Amin, the modulation percentage can also be written as M% = (Amax − Amin) / (Amax + Amin) × 100%. These formulations reflect how deeply the carrier is modulated by the input signal.

In conventional amplitude modulation (AM), the modulation depth is a key design parameter. A modulation percentage of 100% corresponds to full modulation; exceeding 100% leads to overmodulation and envelope distortion, which causes spectral spreading and distortion of the recovered signal. In practice, transmitters often operate below 100% (for example, in the 70–95% range) to balance signal fidelity, regulation, and noise considerations. The concept is less commonly used in frequency or phase modulation, where alternative indices (such as the modulation index in FM/PM) describe the depth of modulation.

See also: amplitude modulation, modulation index, envelope detection.