  Radio observations allow us to identify a wide range of active galactic
nuclei (AGN), which are galaxies that have gas accreting onto the supermassive
black-hole at the centre. By observing these sources at multiple radio
frequencies, a more-complete picture can be built of black-hole accretion
activity. This completeness is aided by radio waves being unaffected by dust
along the line-of-sight to these sources, which cannot be said for waves in the
optical part of the electromagnetic spectrum. (Hence, dust obscuration leads to
biases in AGN samples selected using optical observations.) A thorough
compilation of ~2,000 of the brightest radio-sources in the southern sky [and
so of particular relevance for the Square Kilometre Array (SKA) and its
precursor/pathfinder telescopes] is the GLEAM 4-Jy (G4Jy) Sample, selected at
151 MHz, with subsets being followed up with MeerKAT and the Australia
Telescope Compact Array (ATCA). Meanwhile, optical spectroscopy from the
Southern African Large Telescope (SALT) is being used to derive crucial
redshift information, both for G4Jy sources and for radio-faint AGN in the
MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey.
The origin of the radio emission in these faint sources is a subject of great
debate within the AGN/radio-astronomy communities.
