| 摘要 |
<p>The two-wire duplex data communications system with dc keying has its transmitter (S) consisting of a current-keying switch and its receiver (E) is controlled by the output (AS) of an amplifier (OV). The amplifier is pre-actuated using a voltage derived from the amplifier's supply by means of a voltage divider (R5, R6). The amplifier may be an op. amp. or a diff. amp. followed by a comparator. The receiver is always actuated by a start signal when line continuity is interrupted irrespective of the position of the transmitter.</p> |
