| 摘要 |
PURPOSE:To enable a dial pulse relay on an AC propagation path and to allow even a DP subscriber to receive easily new services by receiving an AC noise caused by disconnecting a DC power source and extracting a voltage level relating to the number of dial pulses and the time factors of the AC noise. CONSTITUTION:The dial pulse generated through user's dial operation is inputted to an interface circuit 2 through the relay line as the AC propagation path. A signal inputted to the interface circuit 2 is a dial pulse AC noise (a), which is inputted to a filter circuit 3. Since the speed of the dial pulse is 10pps or 20pps in the filter circuit 3, only the frequency at the speed is detected and the noise is cut. A next stage voltage level detecting circuit 4 sets a certain voltage width adding the voltage of the dial pulse AC noise (a), and signals at voltage levels other than the said voltage width are considered to be noise. Thus the noise and the dial pulse AC noise (a) are discriminated at two stages of a frequency and a voltage, and the detected dial pulse is counted by a counting circuit 5. |
