| 摘要 |
PURPOSE:To recognize properly a PB signal transmitted by a user from the outside and to eliminate erroneous reception of the PB signal by stopping the detection of the PB signal when it is included in a sound signal transmitted by a self-device and goes around an input line. CONSTITUTION:A sound signal S0 as a guide signal is inputted to a delay device 131 of a receiver 13 and a pushbutton signal component detector 132 from a sound output device 12. A pushbutton signal component PB is included in the sound signal S0. After a certain sensing period expires, the detector 132 outputs a PB signal detection signal S2 to a sound signal suppression device 133 for only a timer tau1. After the sound signal inputted to the delay device 131 passes through an output line l0, it goes around an input line l1 as shown by an arrow alpha and inputted to the suppression device 133 as an input signal S1 and outputted from the suppression device 133 as a S2 obtained by erasing some part of the S2 by the tau1 by means of the detection signal S2. As a result, when the S2 is inputted to a reception pushbutton signal detector 134, the length of a PB' whose some part is omitted is smaller than the sensing time of the detector 134, and a PB reception signal S4 will not rise. |
