Apparatus for use in a communications satellite can include a first mixer arranged to mix and down-convert a received signal in an input frequency range with a first local oscillator LO signal so that a signal within the received signal at a center frequency of a first frequency range is converted to an intermediate frequency IF, a bandpass filter having a passband with a center frequency at the IF arranged to filter the mixed signal such that the filter bandwidth defines the width of the first frequency range, and a second mixer arranged to mix the filtered IF signal with a second LO signal to up-convert the IF signal to an output frequency range. One of the first and second LO signals is a mixed LO signal obtained by mixing the other one with a third LO signal, and the output frequency range is different from the input frequency range.