To solve the problem raised by an SSB transmitter that the center frequency of a BPF which extracts one side of side-band signals from modulated signals obtained by modulating carrier-frequency signals with an inputted voice signal varies depending upon the temperature and a decline in suppression ratio and the deterioration of voices result in.
A microcomputer circuit 23 finds the variation (-Δα) of the center frequency of the BPF 5 from a correction table concerned with the BPF 5 and stored in a ROM 32 based on the temperature information on the BPF 5 detected by means of a temperature sensor 21 and changes the frequency of each signal by -Δα from a reference frequency by controlling local oscillators 4a and 7a which output signals to be modulated and VHF-band signals to a balanced modulator 3 and a mixer 7a. Through this adaptive control, the suppression of carrier signals and the extraction of one side of side- band signals can always be executed in the BPF 5 under the same condition as that in a reference state and a difference component signal generated by a mixer 6 becomes a radio frequency signal of a prescribed frequency. The radio frequency signal is extracted by means of another BPF 8.
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