| 摘要 |
A noise signal filter (5) in a noise level detector (3) filters out the noise signals (Sr) to be determined from a useful signal (Sn) transmitted via transmission channel (1), and mutes the noise signal parts, which have a system reference line as their direct basis, through a rectifier (6) and an amplitude limiter (9) to a peak envelope demodulator (8). The latter produces an envelope curve from the input signal, with places in which only the amplitudes of the noise signal determine the level of the envelope curve. The level of these places is stored by a minimum level memory (11), which follows the input signal, and stores the lowest level value obtained so far. To compensate for a drift of the signal guiding the minimum level memory (11), a second minimum level memory (13) is provided, which stores the lowest minimum value obtained so far and routes it to a signal substracter (16), to compensate for the drift and to remove voltage differences from the tracking to the minimum level memories.
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