A radio receiver configurable to operate in either a low-IF or a zero-IF mode comprises a quadrature down-converter (108,110,112,114) for generating in-phase (I) and quadrature (Q) signals at an intermediate frequency and a complex filter (202) for performing image rejection filtering. One of the outputs (Q) of the filter (202) is terminated, the other (I) is passed to a non-complex ADC (206). The output from the ADC is processed digitally then a quadrature signal generator (212,214) generates quadrature-related IF signals which are passed to a down-converter (216,218) for conversion to baseband signals. By enabling analogue-to-digital conversion and channel filtering to be performed at IF on non-complex signals, significant power savings are possible. Further, the flexibility of the receiver is enhanced, enabling it to operate efficiently in both low-IF and zero-IF modes.