Goal of this project is to study the possible mechanisms of conversion among Stokes parameters and CP generation in radio jets of AGN. When present, the mode conversion is closely related to the properties of the medium crossed by the polarized radiation and suppplies information about the geometry, the strength and orientation of the magnetic field.
A new calibration scheme, allowing the complete description of the 100-m Effelsberg telescope polarimetric response has been developed and a full Stokes polarimetric study of some selected sources have been performed in the range 2.6-10.6 GHz ,with particular attention on Stokes V.
Here we will present the results of our observations and we will show a possible theoretical model that can frame both the observed linear and circular polarization.