| 摘要 |
PURPOSE:To make effective use of radio waves by enabling a receiver to operate intermittently and a transmitter to send out ratio waves only when transmitting a call signal. CONSTITUTION:Receiver part 1 receives a radio carrier which has been modulated by a digital signal containing strings of prescribed pre-ample signals, call signals and end signals. By the outputs of pre-ample signal detection circuit 21 and end signal detection circuit 23 connected to the output, and oscillator circuit 42, gate 43 intermittents the radio wave of receiver part 1 in the normal time and interrrupts the power supply of receiver part 1 by detecting a pre-ample signal, so that the power supply will be disconnected for the time while an end signal is received. As a result, switching circuit 44 intermittents the power supply to receiver part 1, and also transmits the output of call signal detection part 22 to alarm tone generating part 3. In this way, the transmitter is operated only while a call signal is sent out, thereby making effective use of radio waves. |
