PURPOSE:To make a reception beat frequency coincident with a monitor signal frequency, by changing the monitor signal frequency in the equal direction and with the equal amount, when the reception beat frequency is changed with change of the oscillation frequency of BFO. CONSTITUTION:The oscillation frequency fBFO of the BFO5 and a beat detection output fAP are correlated with each other. A beat detector 10 is formed to detect a beat with an osicllation frequency fcar of a transmission carrier oscillator 7 and the fBFO of the BFO5, and the beat detection output fAF as the output is obtained. If the fAF demates a monitor signal, then when a remote station is received with the same pitch as the monitor signal fAF and the signal is transmitted in the state, even if the fBFO of the BFO5 is changed, the frequencies of transmission/reception are coincident with each other.
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