The invention provides an up/down converter with low phase noise. Signals from a first local oscillator are fed through a power splitter to first and second mixers. Signals from a second local oscillator and signals from the power splitter are mixed by the second mixer. The frequency component of the difference between the two signals is removed by a first bandpass filter and passed to a third mixer. Input signals are mixed with signals from the power splitter by the first mixer, and the lower frequency component of the output signals from the first mixer is removed by a second bandpass filter and is passed to the third mixer. Signals from the first and second bandpass filters are mixed by the third mixer. The higher frequency component of the output signals is removed by a low pass filter and is output.