The invention relates to a radio transmitter, including means for up-converting an input signal by mixing the input signal with a local oscillation signal, means for extracting an observation signal from the up-converted signal, means for switching the observation signal between an ON state allowing throughput of the observation signal and an OFF state preventing throughput of the observation signal, means for down-converting the observation signal by mixing the observation signal with the local oscillation signal, means for filtering signal components around the down-converted oscillation signal, means for generating a compensation signal by using the filtered signal in the ON and OFF states of the observation signal throughput, and means for modifying the input signal with the compensation signal.