Abstract: In an antenna matching circuit switching system of a portable telephone, an antenna transmits a transmission signal and receives a reception signal in form of electromagnetic wave. A receiving section receives the reception signal from the antenna and a transmission section supplies the antenna with the transmission signal having a first frequency which is different from a second frequency of the reception signal. A transmission and reception switching section connects the antenna to the receiving section in response to a reception control signal and to the transmission section in response to a transmission control signal. A first antenna matching circuit is matched to the antenna in the second frequency, and a second antenna matching circuit is matched to the antenna in the first frequency.

Abstract: A frequency stabilizing circuit for a .pi./4 QPSK (Quadrature Phase Shift Keying) signal receiver has a voltage controlled oscillator (VCO) for outputting an oscillation signal whose frequency changes in response to a control voltage applied to the VCO. A mixer changes the frequency of an input .pi./4 shift QPSK signal. A counter measures the frequency of the .pi./4 shift QPSK signal from the mixer. A timing generator generates, on the basis of the oscillation signal from the VCO, a timing indicative of an interval during which the counter is to measure the frequency. A set data generator generates a frequency signal having a predetermined set frequency. A comparator compares the frequency measured by the counter and the set frequency of the set data generator to thereby output the resulting frequency deviation. A voltage data generator changes voltage data in association with the frequency deviation. A digital-to-analog converter transforms the voltage data to the control voltage.