Transmitting receiving apparatus

A transmitting-receiving apparatus employing an antenna and comprising:

• control means;
• data processing means controlled by said control means for processing transmitted data and received data so as to be communicated at different timings;
• a transmission-system circuit having an encoder for producing a transmission baseband signal from the transmitted data supplied thereto from said data processing means;
• modulating means for producing a transmitted signal by modulating said transmission baseband signal from said transmission-system circuit;
• a power amplifier for amplifying said transmitted signal;
• a reception-system circuit having demodulating means for producing a reception baseband signal by demodulating a received signal;
• a decoder for producing said received data from said reception baseband signal;
• and
• switch means controlled by said control means for selectively connecting said transmission-system circuit or said reception-system circuit to the antenna, wherein said switch means comprises a first and a second switch and said modulating means has a first oscillator for providing a frequency of said transmitted signal, said demodulating means has a second oscillator for providing a frequency equal to a difference between the frequency of said transmitted signal and a frequency of said received signal, a first mixer for mixing an output supplied thereto from said first oscillator and an output supplied thereto from said second oscillator, a second mixer coupled between said first switch and said demodulating means, and said second switch switches the output of said first oscillator to said second mixer when said first switch connects said reception-system circuit to said antenna and switches an output of said first mixer to said second mixer when said first switch connects said transmission-system circuit to said antenna.