| 摘要 |
<p>PURPOSE:To accurately detect the occurrence of hit even when a carrier level is fluctuated in spite of the hit by detecting the change of a resistance value by the hit of a metallic line. CONSTITUTION:A transformer 1 is inserted between a line 15 and a terminal station 17, and a current is permitted to flow on the lines 13, 15 from a constant current source 2, and a voltage proportional to the resistance of the lines 13, 15 is taken out. The change of a voltage value is detected by an amplifier 3 which inputs a DC voltage proportional to the resistance of a transmission line, a low-pass filter 4 to round a voltage waveform of impulse shape and to make the level of a threshold value easy to decide, an A/D converter 5, a threshold voltage generator 6, comparators 7, 8, and the device of an OR gate 9, and the hit of the line is detected. Thereby, it is possible to accurately detect the occurrence of the hit of not only the transmission signal by a frequency modulation or phase modulation system, but the one by an amplitude phase modulation system or a digital transmission signal system using an OCU (office line terminating device) and a DSU (digital line terminating device).</p> |
