A test setup for testing a contactless digital rotary joint integrated in a device requiring data transmission between a rotating part and a stationary part, the rotary joint further comprises a transmitter and a receiver. The transmitter has a transmitter amplifier, which is coupled to a pair of transmission lines, which are terminated by a pair of terminations. The transmission lines are differential transmission lines comprising a pair of conductors which is driven by differential signals from the transmitter amplifier. The receiver has a receiver antenna comprising a pair of antenna sections which are differentially operated and feed a differential signal to the receiver amplifier. A transmitter ground and a receiver ground are coupled to a common mode signal generator generating a common mode signal. A data source is coupled to the transmitter amplifier feeding a test signal into the transmitter amplifier, and a data sink is coupled to the receiver amplifier for receiving the test signal and generating a test result value. Also disclosed is a method for adjusting a contactless data link integrated in a device requiring data transmission between a rotating part and a stationary part.