A radio receiver is configurable to operate in both low-IF and zero-IF modes with maximum re-use of of analogue and digital circuitry between modes. The receiver comprises a quadrature down-converter for generating in-phase (I) and quadrature (Q) signals at an intermediate frequency and a complex filter for performing image rejection filtering. In the low-IF mode, one of the outputs (Q) of the filter is terminated, the other (I) is digitised by a non-complex ADC then the digital signal is filtered and decimated. Quadrature-related IF signals are then re-generated before down-conversion and demodulation. In the zero-IF mode, both outputs of the filter are digitised and processed in parallel before demodulation. By enabling analogue-to-digital conversion and channel filtering to be performed at low-IF on non-complex signals, use of just two non-complex ADCs is possible, thereby avoiding duplication of circuitry and providing significant power savings.