  It has been proposed recently that the SKA1-MID could be used to conduct an
HI intensity mapping survey that could rival upcoming Stage IV dark energy
surveys. However, measuring the weak HI signal is expected to be very
challenging due to contaminations such as residual Galactic emission, RFI, and
instrumental 1/f noise. Modelling the effects of these contaminants on the
cosmological HI signal requires numerical end-to-end simulations. Here we
present how 1/f noise within the receiver can double the effective uncertainty
of an SKA-like survey to HI on large angular scales (l < 50).
