Abstract: A radio frequency FET amplifier has an FET which commonly amplifies a plurality of radio frequency signals and a bias power supplying circuit which varies bias power supplied to the FET according to the number of inputted radio frequency signals. A DC/DC converter controls supply voltage according to control voltage corresponding to the number of inputted radio frequency signals, thus generating a converter output voltage proportional to the control voltage. A constant current circuit supplies drain voltage substantially equal to the voltage to the drain terminal of the FET and also supplies gate voltage to the gate terminal of the FET so as to hold the drain current therein substantially constant. Power consumption is reduced depending on changes in the number of inputted radio frequency signals, while suppressing variations of harmonic distortion component peak level and frequency characteristics.

Abstract: In a radio blind zone system, a master unit and a slave unit are respectively situated at an existing station and a radio blind zone and connected together by a coaxial transmission path. The master unit feeds a load current to the slave unit which includes a relay amplifying device or a tower-top amplifying device. The master unit is capable of detecting an error occurred in the slave unit by detecting a change in the load current applied to the slave unit.

Abstract: A frequency synthesizer is disclosed which has a PLL (Phase Locked Loop) made up of voltage controlled oscillator (VCO), variable frequency divider, phase comparator, charge pump, and loop filter. A reference signal source feeds a reference signal to the phase comparator and comprises a reference signal oscillator and a fixed frequency divider. A first and a second waveform converting circuit each divides respective comparison outputs of the phase comparator to produce a charge control signal voltage and a discharge control signal voltage meant for the charge pump. The division of the output periods of the comparison outputs successfully reduces spurious components which are apart from the center frequency of the synthesizer by integral multiples (inclusive of 1) of the reference frequency.

Abstract: A frequency synthesizer comprises a voltage controlled oscillator, and a variable frequency divider for dividing the VCO frequency according to the frequency of a communication channel. The output of frequency divider is compared with a reference frequency and a phase difference of first polarity and a phase difference of second polarity are detected. A charge-control voltage is generated with a duration variable with the phase difference of first polarity and a discharge-control voltage with a duration variable with the phase difference of second polarity. First and second integrators are coupled respectively to outputs of the phase comparator for respectively smoothing waveforms of the control voltages. Energy is injected into a charge pump in response to the smoothed charge-control voltage and drained from it in response to the smoothed discharge-control voltage to produce a frequency control signal for coupling to the VCO.

Abstract: A linear amplifier performing a continuous distortion compensation control without no line cut to prevent deterioration of intermodulation distortion and ensure talking quality including a power amplifier for amplifying a plurality of carriers and a distorter for generating an intermodulation distortion with an equal amplitude of an antiphase for negating an intermodulation distortion generated by the power amplifier. A processing unit outputs an attenuation value control voltage and a phase control voltage to the distorter depending on an ambient temperature information detected by a temperature sensor and control voltage data corresponding thereto, read out of a memory.