Modulationsgrad

Modulationsgrad, in German technical usage often referred to as modulation depth, is a dimensionless measure of how strongly a carrier signal is varied by its modulating signal. It is most commonly used in amplitude modulation (AM) to describe how much the envelope of the carrier swings.

Formally, for an AM signal we can write s(t) = A_c [1 + μ m_norm(t)], where A_c is the carrier amplitude, m_norm(t) is the normalized modulating signal with maximum absolute value 1, and μ is the Modulationsgrad. When the modulating signal is a sinusoid, μ equals the modulation index; for a sine wave of peak amplitude M and linear modulation, μ = k_a M. The practical range is 0 ≤ μ ≤ 1; μ = 1 corresponds to 100% modulation and μ > 1 leads to overmodulation and distortion.

In the time domain the envelope varies between A_c (1 − μ) and A_c (1 + μ). From envelope measurements, μ can be computed as μ = (A_max − A_min) / (A_max + A_min), with the percent modulation equal to μ × 100%. In the frequency domain, the AM sidebands have amplitude (μ A_c)/2 each, while the carrier remains at A_c; the sideband-to-carrier ratio is μ/2.

Besides AM, the concept of modulation depth can be extended to other modulation schemes, though the exact definition differs (for FM, the modulation index β relates to peak frequency deviation). In engineering practice, Modulationsgrad helps quantify signal quality, determine overmodulation risk, and set transmitter levels. See also Modulation depth, Modulation index, Amplitude modulation.