| 摘要 |
PURPOSE:To detect both open subscriber line and short-circuit by means of a supervisory device by providing a circuit short-circuiting intermittently the 1st and 2nd lines at a radio terminal device side from the 1st diode and opening the switch circuit in response to a current so as to close the circuit when no current flows. CONSTITUTION:When a check signal of a subscriber line 12 is inputted from a supervisory device 3 to a radio connection device 4, the radio connecting device 4 modulates the check signal by using a radio frequency and transmits the modulated signal to a radio terminal device 6. A transmission/reception circuit 7 transmits a polarity inverting signal to a polarity setting circuit 10 via a signal line 71. The polarity setting circuit 10 receiving the polarity inverting signal inverts the polarity of the output voltage from the normal operating state. The relation of V1<V2 exists in the inverted state and a current flows to an output line L4 of a power supply circuit 9. Then a switch circuit 15 opens the circuit, no current flows, the switch circuit 15 closes again the circuit and then a current flows. Thus, the current flows intermittently, a current detection circuit 11 detects the intermittent current so as to detect that the subscriber line 12 is normal. |
