Wideband untuned baseband receivers incorporating high-resolution digitisers and polyphase digital filter banks (PDFBs) have been proposed for SKA and LOFAR, and PDFBs are being actively developed as core elements of beamformers, spectrometers and cross correlators for a number of other radio telescopes. Early on-air test results of a 1024-channel, 0-256 MHz baseband receiver, demonstrate excellent spectral purity and robustness against strong in-band RFI.