Intermodulationsverzerrungen

Intermodulation refers to a nonlinear phenomenon in which a system that does not respond linearly to multiple input signals generates additional frequencies, known as intermodulation products, that were not present in the inputs. This distortion arises when the system’s transfer characteristic includes nonlinear terms, causing the output to contain products of the input signals.

In a simple description, if two tones at frequencies f1 and f2 pass through a nonlinear device, the output contains not only the original tones but also new frequencies formed by combinations of f1 and f2, such as f1, f2, and sums and differences like f1 ± f2, 2f1 ± f2, and so on. The third-order intermodulation products, particularly those near the original carriers (for example 2f1 − f2 and 2f2 − f1), are of special practical importance because they can interfere with adjacent channels in communications systems.

Intermodulation distortion (IMD) is a key concern in radio frequency, telecommunications, and audio equipment. In RF systems, IMD can degrade adjacent-channel performance and reduce receiver sensitivity. In audio, IMD can produce audible artifacts when multiple tones interact within amplifiers or loudspeakers.

Measurement of intermodulation often uses a two-tone test, with signals at f1 and f2, and the strength of the intermodulation products expressed as dBc relative to the carrier tones. Mitigation strategies include operating devices in their linear region, applying predistortion or feedback linearization, improving impedance matching, and employing filtering and isolation to suppress generated intermodulation products.