| 摘要 |
PURPOSE:To discriminate securely a data and a voice signal by superposing the voice signal with a specific AC signal having a frequency band which is within the use-limit frequency band of a communication circuit using the AC signal and never used by modem and transmitting the result. CONSTITUTION:The signal of a specific AC signal generating circuit 12 is superposed upon the voice signal of a microphone 10. This signal has frequencies in frequency bands C and D obtained by excluding a frequency band B for data transmission and reception from the frequency band A of the communication circuit (c), and 11 is a switching circuit which is associated operatively with the talk switch of the microphone 100. The detecting circuit 2 detects the specific AC signal from another transmitter and receiver. An SW3 supplies a receive input from a hybrid coil (HYB)1 to a modem 5 only when there is not said detection output. An SW4 supplies the receive input to a BPF6 only when the detection output is present. Thus, a data signal when sent is inputted to the modem 5 through the HYB1 and SW3. When the voice signal is sent by interrupting data transmission, it is supplied to the BPF6 through the HYB1 and SW4 and only the voice signal is received. |
