Abstract: A radio transmission/reception system using the same frequency includes a power control circuit which can prevent a sensitivity of the receiver from being lowered due to the carrier radiated from the transmitter, and finely control the power. The power control circuit includes first and second variable attenuators being respectively installed at an intermediate frequency stage and a local oscillator frequency stage, so as to finely control the power level of a next radio frequency stage. A CPU (central processing unit) controls amounts of attenuation of the first and second variable attenuators.

Abstract: A transmission and reception method and apparatus is capable of supplying local oscillation frequencies for upconversion and downconversion, as well as carrier frequencies for modulation and demodulation by utilizing only one local oscillator. The apparatus includes a reference signal generator for generating a reference signal, and a phase locked loop for locking the output of the reference signal generator to a predetermined frequency. A signal generator generates a signal in response to the output provided from the phase locked loop, and provides the signal to phase shifters in modulation and demodulation circuits. A first frequency multiplier multiplies the output of the signal generator, a first band pass filter band pass filters the output of the first frequency multiplier, and a first amplifier amplifies the output of the first band pass filter and provides the amplified result to an upconversion mixer.