| 摘要 |
PURPOSE:To prevent simultaneous interception for two-way taking in monitoring an outgoing channel by using a talking busy signal sent from a mobile set side at the transmission of a mobile set so as to increase the return loss of the exchange side. CONSTITUTION:A transmission sound signal from a microphone 5 is inputted to a vogad amplifier 6 in a mobile set 1, and the output of the amplifier 6 is sent to an incoming channel via a synthesizing amplifier 9 and a transmitter/ receiver 10. When the output of the amplifier 6 is detected by a detector 7, a talking busy signal in a specific frequency (e.g., 3.5kHz) is inputted to the amplifier 9 from a talking busy signal generator 8 and the signal is sent while being superimposed on the sound signal. A radio base station 3 demodulates the reception signal of the incoming channel onto the sound signal and amplifies (11) the result and a taking signal blocking circuit 12 eliminates the talking busy signal in the specific frequency and applies the result to a hybrid transformer 16. The talking busy signal passes through a BPF 13 and detected by a detector 14. The detection signal of the detector 14 controls an automatic attenuator 15 inserted in the outgoing transmission circuit from the transformer 16 to increase the attenuation. |
