A signal generator is disclosed that generates a test signal to be applied to a first and second wire of a subscriber line. The signal generator is configured to generate the test signal at the first and second test signal outputs in a first time section such that a first potential at the first test signal output is changed from a first value to a second value and a second potential at the second test signal output is maintained constant at least during the change of the first potential. The signal generator is further configured to generate the test signal during a second time section such that the first potential at the first output and the second potential at the second output are oscillating with a predetermined frequency.