Timing residuals plotted against wavelength squared for simulated SKA-Low data. Upper panel: Timing residuals for a chosen epoch perturbed by SDDS and TDDS different sub-integration times T. For T = 10, 15, 30 s, the effect of SDDS prevails the TDDS and the residuals are consistent; while for T = 100 s, the TDDS dominates and distorts the signal at lower part of the frequency band (see Fig. 13) and increases the residuals. Lower panel: Timing residuals for T = 10 s dominated by the SDDS. The colours correspond to different orbital phases ψ. Grey lines illustrate the theoretical magnitude of the SDDS predicted by Eq. (15).