Radio observations allow us to identify a wide range of active galactic nuclei (AGN), which play a significant role in the evolution of galaxies. In the first part of this talk, I will escribe a new sample of powerful radio-galaxies, whose bright emission is detected at low radio-frequencies by the Murchison Widefield Array (MWA). This covers 72-231 MHz, and the 20 flux-densities over this range enable their broad-band radio spectra to be studied. Doing so highlights 'restarted' radio-galaxies, relic radio lobes, and sources with a spectral turnover that is likely due to free-free absorption by ionised gas. Identification of host galaxies is now complete, making this a highly-valuable legacy dataset. For the remainder of my talk, I will present recent analysis of radio emission from ‘radio-quiet’ quasars (RQQs). Being at low radio-luminosities, it has been assumed that their emission is dominated by star formation. However, using multi-wavelength data for two samples, we find support that black-hole accretion makes a significant contribution to the total radio emission in RQQs. These studies have important implications for modelling AGN feedback, and for determining the accretion and star-formation histories of the Universe.