| 摘要 |
PURPOSE:To enable measurement for the reception sensitivity level of the data communication unit from a remote location, by forming the returned loop with the instruction from the center of other terminal. CONSTITUTION:When the loop back test instruction is made from the control unit 11 of the data communication unit 10 at the ceter side, after it is demodulated at the demodulation circuit 24 of the data communication unit 20 at the terminal via the data line 30 through the modulation at the modulation circuit 12, it is detected at the control unit 21 to form the returned tool to the inside of itself and the modulation circuit 22 is operated by turning on the RS signal based on the DC signal received from the carrier detection circuit 27 and the test pattern fed continuously from the center is fed back to the center via the data line. When the transmission level at the center side is gradually reduced by controlling the variable attenuator 18, it is judged as reception interruption at the circuit 27 at the terminal 20 and when the CD signal is OFF, RS signal is OFF to stop the return to the center and the reception sensitivity level can be calculated at the center from the transmission level in this case. |
