Abstract: Received signal inputted from an antenna 1 is fed via a received signal mixer 2 and an A/D converter 3 to a demodulator 4. The demodulator 4 is operated according to software down-loaded in a software memory 5 from a program memory 6. A demodulator output digital signal is fed to a base-band signal processor 8 for signal processing, and then fed out through a man-machine interface 9 to the outside. On the transmission side, a signal to be transmitted is inputted to a modulator 10 though a route converse to that of the received signal. The modulator output is fed to a D/A converter 11 for conversion to an analog signal, which is in turn fed to a transmission signal mixer 12 for conversion to a carrier frequency, and then fed to a module, which includes a power amplifier 21, a transmission signal filter 22 and an isolator 23, to be transmitted via the antenna 1.

Abstract: To obtain a radio set in a direct conversion system so as not to have any undesired influence of a signal of a transmission system on a reception system. In a transmission system, a frequency Flo of a local signal used in a frequency converting process performed by a frequency converter is expressed as (M/N)·Frx by a frequency conversion circuit. Based on the frequency Flo and the transmission frequency Ftx, a intermediate frequency Ftxif of the transmission system is expressed as Ftxif=Flo?Ftx=(M/N)·Frx?Ftx which is an oscillation frequency of a second local oscillator. Therefore, an equation exists as Ftx+Ftxif={(M/N)·Frx?Ftxif}+Ftxif=(M/N)·Frx, although Ftx+Ftxif leak to the reception system. As a result, since it is different from a reception frequency band, no interference wave is generated for a received signal.

Abstract: A direct conversion receiver corrects the phase of a signal when the gain of a low-noise amplifier is switched. A complex multiplier sets, in advance therein, the amount &Dgr; of a shift of the phase which is caused when the gain of the low-noise amplifier is switched. Depending on the gain of the low-noise amplifier which is switched by a gain switching signal, the complex multiplier corrects the phase of a baseband signal from an A/D converter by the preset amount &Dgr; of the shift. By correcting a phase change in the low-noise amplifier which is caused when the gain of the low-noise amplifier is switched, the phase state of baseband I, Q signals can be held in a state prior to the switching of the gain to prevent the bit error rate (BER) of a received signal from being degraded.

Abstract: To obtain a radio set in a direct conversion system so as not to have any undesired influence of a signal of a transmission system on a reception system. In a transmission system, a frequency Flo of a local signal used in a frequency converting process performed by a frequency converter is expressed as (M/N)·Frx by a frequency conversion circuit. Based on the frequency Flo and the transmission frequency Ftx, a intermediate frequency Ftxif of the transmission system is expressed as Ftxif=Flo−Ftx=(M/N)·Frx−Ftx which is an oscillation frequency of a second local oscillator. Therefore, an equation exists as Ftx+Ftxif={(M/N)·Frx−Ftxif}+Ftxif=(M/N)·Frx, although Ftx+Ftxif leak to the reception system. As a result, since it is different from a reception frequency band, no interference wave is generated for a received signal.

Abstract: A portable radio communication apparatus, includes a main body, and a sub-apparatus. The main body communicates with a partner. The sub-apparatus is mechanically separated from the main body. The main body and the sub-apparatus communicate with each other wirelessly. The sub-apparatus includes a call signal arrival display unit and a response unit. When the main body gets a call signal from the partner, the main body transmits a call arrival signal to the sub-apparatus. The main body transmits a response message to the partner in response to a response signal. The call signal arrival display unit sends a notice that the main body gets the call signal in response to the call arrival signal. The response unit outputs the response signal to the main body in response to an operation performed on the response unit.

Abstract: A direct conversion receiver comprising mixers for mixing a received radio frequency signal and a local oscillation signal in frequency, a signal processing unit for converting the output signal of the mixers into a baseband signal, a delta-sigma modulator for detecting offset voltage from the output signal of the signal processing unit, a holding circuit for supplying offset canceling voltage for canceling the offset voltage, and a switch of supplying the output signal of the mixers to the delta-sigma modulator during a given period and supplying the offset canceling voltage sent from the holding circuit to the output side of the mixers.

Abstract: The invention provides a transceiver in which a mutual interference between the transmitting and receiving circuits can be suppressed, without a shielding plate therebetween. The transceiver comprises the first and second printed circuit boards, which are positioned face to face. Components of the transceiver are mounted on the front surfaces of the aforementioned printed circuit boards, and compose the transmitting and receiving circuits. The front surfaces of the first and second boards are respectively divided into the transmitting and receiving regions As and Bs, on which corresponding components are respectively mounted. The aforementioned regions As and Bs are so formed that they are respectively positioned face to face, then the components of the transmitting and receiving circuits are never positioned back to back, and the mutual interferences between the transmitting and receiving circuits does not occurs, even if a shielding plate is eliminated.

Abstract: A radio transmitter has an output power control circuit including a power amplifier, a directional coupler coupled to the power amplifier, a detector of the forward power of the directional coupler, a generator of a difference voltage between the output voltage of the detector means and a reference voltage. A power regulator varys the output power of the power amplifier in response to the output of the difference voltage. The power applied from the power amplifier through the directional coupler to the detector is controlled by a control signal.The control circuit electrically varies the coupling coefficient of the directional coupler for attenuating the power applied from the directional coupler to the detector means to extend the controllable range of the transmitter output power.