Radio spectra over the ∼0.1 − 10 GHz observed frequency range of the three sources described in this work. The rest-frame frequencies (top labels) were computed assuming a common redshift, z = 5.6, for all the three objects. The majority of the data points are from public surveys (circles), while the 2.1, 5.5 and 9 GHz measurements are from dedicated, simultaneous observations with ATCA (squares). The dashed line in each panel indicates the best-fit model obtained for the different objects as described in the text. The dotted line in the central panel corresponds to the best-fit power law obtained from the GLEAM-X data only, while the dotted and the dashed-dotted lines in the top panel show the two spectral components used during the fit, as described in the text.