Proper motion of reference radio sources

The motion of relativistic jets from the active extragalactic nuclei can reach several hundred microseconds per year and mimic proper motion of the distant radio sources observed by VLBI. Such motion of individual quasar is not correlated and its magnitude exceeds the small systematic effects induced by the rotation of the Solar system around the centre of the Galaxy. In this paper we search for the cause of the systematic effect and discuss the results.