| 摘要 |
PURPOSE:To permit the respective kinds of balance of voice quality with noise and sensitivity at the time of a stereo voice signal to be satisfactory and to enhance conversion efficiency and reception sensitivity by converting a voice signal into an optical signal in a QPSK-modulated state so as to execute optical space transmission. CONSTITUTION:In a transmission system 31, an intermediate frequency signal adding a video signal and a voice subcarrier signal which is made into QPSK are supplied from a BS tuner 3. Then, the QPSK-modulated voice subcarrier signal from BPF 33 is impressed on the parallel circuit of a proper number of infrared ray LEDs 35 and a resistor. Therefore, the voice signal is converted into the optical signal in the QPSK-modulated state and optical space transmission is executed. In the reception system 32, the QPSK-modulated voice subcarrier from the connection center point of a photodiode 36 and the resistor 37 is supplied to a demodulator (four phase PSK demodulation) 40 with BPF 39 so as to be QPSK-demodulated. Then, a digital stereo voice signal is obtained by a decoder (PCM demodulation). |
