Spectral configurations assuming a 4−18 GHz IF band that allow the simultaneous observation of low density tracers (¹²CO(1–0), ¹³CO(1–0), and C¹⁸O(1–0)), and tracers of dense gas (CS(2–1), C³⁴S(2–1), ¹³CS(2–1), N₂H⁺(1–0), HNC(1–0), HCO⁺(1–0), and HCN(1–0)) for a range of redshifts. The vertical black lines indicate the position major spectral lines with each horizontal row corresponding to the redshift (z) indicated. The corresponding coloured bars show the sky frequency coverage of the upper and lower sidebands for the LO frequency indicated by the coloured cross. The solid blue curve shows the zenith atmospheric transmission at ALMA for a PWV value of 2 mm. Figure adapted from Mroczkowski et al. (2019a).