| 摘要 |
PURPOSE:To economize considerably the PB signal receiving system by detecting only one wave of a PB signal in accordance with each channel and connecting this channel to a common installed PB signal receiving circuit through a channel switch in accordance with the detection result. CONSTITUTION:A frequency detecting circuit DET4 using zero-crossing count detects only 941Hz of a low group frequency assigned to PB signals ''*'', ''0'', and ''#''. A PCM coded call signal (consisting of 7 signal bits 401 and one sign bit 402) is inputted from an ICT3 to a buffer circuit 40. If a level detecting circuit 41 confirms that this call signal has a certain level or higher, the state of the sign bit 402 is inputted to a counter 43 through an AND gate 42 and is counted from a prescribed time. It is confirmed by a frequency discriminating circuit 44 that the counted value is 941Hz, and the connection time is confirmed by a timer circuit 45 to detect the coming of the 941Hz signal, and this coming is reported to a CP7. |
