Continuous electric power supply, which is transferred from the contact wire to the train through a pantograph mechanism, is a necessity for a train to function satisfactory. Since various sources of nonlinearities are present, such as friction in the pantograph suspensions and impacts in the subsystems and at the excitation, there is a possibility of nonlinear dynamic behaviour. The aim of this work is to experimentally investigate the dynamic behaviour of a commercial pantograph to verify if nonlinear behaviour and coupling effects can occur. A test rig has been built that has the ability to simulate both the horizontal and vertical excitation generated by the contact wire. Measurements have been performed for sinusoidal input signals both in horizontal and vertical directions. Harmonic and subharmonic motions as well as irregular behaviour are shown to exist in the system. The results show that the pantograph's rotational degree of freedom, friction in the suspension systems and the nonlinear stiffness play an important role for the dynamic behaviour of the system and are therefore crucial to include when creating mathematical models of the system.