| 摘要 |
PROBLEM TO BE SOLVED: To provide a television doorphone device which can detect master machine which is located at the farthest end. SOLUTION: A television doorphone device detects whether a cable 3 is connected to the terminal 52 of a master machine 2 by means of a cable connection detector 53 and closes a terminating switch 54 for connecting the cable 3 by means of terminating equipment 56, according to the detecting output of the detector 53. Opening/closing state of the switch 54 is detected by means of a termination detector 55, and the signal level in the opened/closed state of the switch 54 is detected by means of a signal level detector 57. Impedances of the cable 3 and terminating equipment 56 are automatically adjusted, so that the signal level when the switch 54 is closed becomes one half that of the signal level, when the switch 54 is opened.
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