A measuring system (1) comprises a signal generator (2), generating a digital modulated high frequency measuring signal (MS), for supplying to the input (4) of a test unit (4). A signal analyser (5) connected to the output (6) of the test unit (4), analyses the output signal (OS) of the test unit (4) after a demodulation. A direct connection (7) is provided between the signal generator (2) and the signal analyser (5), by means of which a reference signal (Ref) is supplied directly to the signal analyser (5) from the signal generator (2).