SEDs of the 18 BAL QSOs observed during the m/mm-wavelengths campaign (x-axis: GHz; y-axis: mJy). 235 MHz and 610 MHz flux densities from the GMRT; 250 GHz flux densities from IRAM-30 m; 345 and 850 GHz flux densities from APEX. Measurements at other frequencies are taken from Bruni et al. (2012), or from our polarimetry campaign (see Sect. 3). Triangles are 3σ upper limits. Solid lines are parabolic or linear fits, according to the criteria discussed in Sect. 4.2.