A device for measuring an optical transmission path, comprising - at least one measurement transmitter (H1,H2,H3) for transmitting an optical measurement signal, - at least one receiver for receiving an optical signal, - a driving and evaluating unit which is connected to the at least one measurement transmitter (H1,H2,H3) and to the at least one receiver and is operative to drive the at least one measurement transmitter (H1,H2,H3) and to process and evaluate the optical signal received by the at least one receiver for use as an electric measurement signal, - wherein the driving and evaluating unit comprises at least one measurement amplifier (18,19) which has a preferably settable input-signal-amplitude nominal range or nominal level and which, in case of an input signal having an amplitude within the nominal range and respectively equal to the nominal level, is neither over-amplified nor underamplified and thus provides an amplified output signal that is within a signal range defined by an upper and a lower limit, - wherein the driving and evaluating unit comprises a detector for detecting overamplification and/or underamplification and/or for detecting a non-performed overamplification and/or underamplification of the at least one measurement amplifier (18,19) by comparing the output signal of the at least one measurement amplifier (18,19) to both said upper and said lower limit, and is operative to evaluate the quality of the measurement signal on the basis of detection signals output by the detector and/or of detection signals output by the detector as observed during a monitoring phase, and - at least one interference radiation compensation unit (26,27,28,29) comprising at least one compensation transmitter for generating a compensation signal for the receiver or for the electric signal delivered by the receiver, - wherein the driving and evaluating unit comprises a detector for detection of a parameter representing the compensation signal, characterized in - that the driving and evaluating unit is operative, upon detection of a temporal pattern of underamplification and/or overamplification of the at least one measurement amplifier (18,19) as detected by the detector during a monitoring phase, and, if detected, of the parameter of the interference radiation compensation unit (26,27,28,29), to drive the at least one measurement transmitter (H1,H2,H3) and the interference radiation compensation unit (26, 27,28,29) or the at least one compensation transmitter thereof in a manner modified relative to the monitoring phase by use of a transmission signal and a compensation signal which is orthogonal to the pattern by having a frequency different from the frequency of the pattern, or by having a spread spectrum code or by being frequency-band-restricted, wherein the frequency of the pattern is not included in the frequency band of the pattern. - at least one measurement transmitter (H1,H2,H3) for transmitting an optical measurement signal, - at least one receiver for receiving an optical signal, - a driving and evaluating unit which is connected to the at least one measurement transmitter (H1,H2,H3) and to the at least one receiver and is operative to drive the at least one measurement transmitter (H1,H2,H3) and to process and evaluate the optical signal received by the at least one receiver for use as an electric measurement signal, - wherein the driving and evaluating unit comprises at least one measurement amplifier (18,19) which has a preferably settable input-signal-amplitude nominal range or nominal level and which, in case of an input signal having an amplitude within the nominal range and respectively equal to the nominal level, is neither over-amplified nor underamplified and thus provides an amplified output signal that is within a signal range defined by an upper and a lower limit, - wherein the driving and evaluating unit comprises a detector for detecting overamplification and/or underamplification and/or for detecting a non-performed overamplification and/or underamplification of the at least one measurement amplifier (18,19) by comparing the output signal of the at least one measurement amplifier (18,19) to both said upper and said lower limit, and is operative to evaluate the quality of the measurement signal on the basis of detection signals output by the detector and/or of detection signals output by the detector as observed during a monitoring phase, and - at least one interference radiation compensation unit (26,27,28,29) comprising at least one compensation transmitter for generating a compensation signal for the receiver or for the electric signal delivered by the receiver, - wherein the driving and evaluating unit comprises a detector for detection of a parameter representing the compensation signal, - that the driving and evaluating unit is operative, upon detection of a temporal pattern of underamplification and/or overamplification of the at least one measurement amplifier (18,19) as detected by the detector during a monitoring phase, and, if detected, of the parameter of the interference radiation compensation unit (26,27,28,29), to drive the at least one measurement transmitter (H1,H2,H3) and the interference radiation compensation unit (26, 27,28,29) or the at least one compensation transmitter thereof in a manner modified relative to the monitoring phase by use of a transmission signal and a compensation signal which is orthogonal to the pattern by having a frequency different from the frequency of the pattern, or by having a spread spectrum code or by being frequency-band-restricted, wherein the frequency of the pattern is not included in the frequency band of the pattern.