| 摘要 |
PURPOSE:To prevent radio interference with other telephone set by coupling telephone set circuits partially through a free space transmission line for light-amplitude- modulated signals. CONSTITUTION:A calling signal sent from telephone exchange 1 is radiated into the free space as light-amplitude-modulated signal 31 by way of detecting circuit 7 and optical signal transmitter 12. Signal 31 is received by reveiver 23 in mobile telephone set 3. As an answer is made with hook switch 24 off the hook, an answer signal is radiated from transmitter 20 as optical signal 28 and then received by receiver 15 in fixed telephone set 2. Similarly, transmitters 22 and 14 and receivers 21 and 13 are provided for transmission and reception of aural signals. Therefore, since light is used as a transmission medium, the need for countermeasures to radio interference with other telephone sets in eliminated and employing the amplitude modulation system amplifies the constitution. |
