Dust and synchrotron B-mode power versus frequency for two multipole bins: ℓ = 4–11 (top) and 60–79 (bottom). The coloured bands show the range of power measured from the smallest (LR24) to the largest (LR71) sky regions in our analysis. The lower limit of the synchrotron band is derived from the S-PASS data analysis in Krachmalnicoff et al. (2018). The primordial CMB B-mode signal, averaged within the appropriate ℓ bin, is plotted with dashed lines for three values of the tensor-to-scalar ratio: r = 0.1; 10⁻²; and 10⁻³. The solid line represents the lensing B-mode signal for the Planck 2015 ΛCDM model (Planck Collaboration XIII 2016).