A useful electrical signal is a signal that occurs during electrical data transmission and is used for useful purposes, which is characterized by special electrical quantities such as voltage , current , frequency , etc. According to the special characteristics, a distinction is made, for example, between useful voltage signal, useful current signal, etc. The useful signal can consist of a time-continuous or time-discrete process. In the case of the assignment of the useful signal to a reference value , one speaks of a useful level , which represents a significant quantity of the electrical useful signal. The counterpart of the useful signal is the interference signal .
A pure and simple useful signal is z. B. a sound or audio signal , which is picked up by a microphone, processed by an electronic circuit and later played by a loudspeaker (to the user). A picture signal ( FBAS ), on the other hand, has a complicated structure; it contains the actual picture content as a useful signal ( also called line content in television technology ) and the synchronous signals as additional or control signals.
In the case of technical communication , one is interested in the useful signal reaching the receiver as strong and undistorted as possible . For this it is necessary that any interfering signals that may occur are as weak as possible so that they do not impair the useful signal.