Abstract: A device for detecting co-channel interference in transmitted signals having sync pulses is disclosed, characterized in that the detected interference may be measured. The apparatus includes a detector for detecting the sync pulses, and measuring apparatus for determining a change in amplitude of the sync pulses. The measuring apparatus comprises a sampling device responsive to the detector for producing a signal indicative of the amplitude of each sync pulse. A first output is produced indicating the sum of two successive signals and a second output is produced indicating the difference of two successive signals. An analogue to digital converter produces a digital representation of each of the first and second outputs, respectively, which representations are converted to digital signals an arithmetic device. The digital signals are indicative of the magnitudes of the signals produced by the sampling device. A subtraction device subtracts the digital signals from each other to produce a control signal.