| 摘要 |
PURPOSE:To limit a sound signal without exerting any influence on data signal at all by varying an amplitude limiting value so that the amplitude limiting value is greater when the data signal and the sound signal are transmitted and received than when dial pulses are transmitted and when a ringer is received. CONSTITUTION:A carrier detection signal input terminal 9 is connected to data modems 5-1, 5-2...5-m, 5-n. The modems when receiving the data signal detect a data carrier frequency to send detection signals to the terminal 9. Each detection signal is inputted to a control circuit 8. The control circuit 8 closes a switch S to connect a capacitor C2 to a capacitor C1, so the impedance values of the capacitors decrease to limit the amplitude of the sound signal to the extent where no influence is exerted on the data signal. When dial pulses and a ringer are inputted, none of the modem detects a carrier, so the capacitors C2 and C1 are not connected in parallel. Consequently, the impedance of the capacitor C1 is increased to the extent where no influence is exerted on the dial pulses and ringer. |
