Interfering signal

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A noise , Eng. interfering signal is a signal that occurs unintentionally as a stray signal due to capacitive , inductive or galvanic coupling on the lines . The opposite of interference signal is the useful signal . Targeted jamming transmissions are known as "jamming"; they can be used as electronic countermeasures to prevent the spread of unwanted messages.

Interference signals are generated, on the one hand, by crosstalk (crosstalk) from neighboring lines and, on the other hand, by external EMC influences (electromagnetic compatibility). Interference signals impair the received signal behavior, which is why one tries to prevent or reduce these signals and, above all, their irradiation through targeted cable construction .

With shielded cables, the external influence is so small that it can be neglected. In the case of unshielded cables, however, neighboring signal lines can have an additional negative impact on the attenuation-to-crosstalk ratio ( ACR = attenuation to crosstalk ratio ).

In the case of asymmetrical cables such as coaxial cables , the interference is diverted via one or more shields. With symmetrical data cables ( twisted pair ), the interference signals are compensated for by a completely symmetrical cable structure. The structure of the cores is chosen so that interference signals interspersed by the stranding of the cables occur in the same strength on both lines and the receiver only receives the difference between the interference signals. In practice, however, this only applies to a limited extent, so the EMC stability must either be improved by a shield, or the area of ​​application is selected so that the twist is sufficient.


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  • Paul Profos, Tilo Pfeifer (Ed.): Basics of measurement technology. R. Oldenbourg Verlag, Munich / Vienna 1997. ISBN 3-486-24148-6
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