Polarization characteristics of the reference source (Source 07). Stokes Q and U intensities, polarized intensity P and polarization angle χ are shown as a function of frequency and wavelength squared λ² (bottom and top axes) for the reference epoch (in black, first two rows), and for the stacked data from Cycle 2, (in blue, third and fourth row) and from Cycle 4 (in orange, two last rows). The scatter in the data is reduced by stacking. The effect of Faraday rotation is clearly visible in the variations of Q, U and χ; the decrease of the polarized intensity with λ² is an indication of Faraday depolarization. The final combination of Cycle 2 and Cycle 4 data is done in Faraday depth space, as described in the text.