The invention comprises a frequency converter for converting an input frequency to an output frequency where the frequenicies are widely separated. The system includes a free running output oscillator adapted to be injection locked to an output frequency. A local oscillator having a frequency near the output frequency, has its signal mixed with the input frequency to obtain a signal containing sideband frequencies which are both above and below the local oscillator frequency. Means are provided for separating the sideband frequencies and applying one of the sidebands as an injection locking signal to the free running oscillator. In the preferred embodiment, the bandwidth of the free running output oscillator is centered above the highest sideband frequency if the sideband is lower in frequency than the frequency of the local oscillator or is centered below the lowest sideband frequency is the sideband is higher in frequency than the frequency of the local oscillator.