| 摘要 |
The method involves encoding a frame in a succession of multifrequency signals. Each signal consists of two frequencies from a predetermined set, with each pair having a duration at least five times the period of the lowest frequency and forming the elementary unit of information. This primary signal frequency modulates a high frequency carrier which is applied to the electrical network. Each receiver (R) demodulates the signal and checks the address prior to validating the action. The receiver at the correct address returns a high frequency carrier, modulated by a signal identical to that emitted. This prompts the display of a message for a successful execution. Should the reply not arrive, the order is repeated. On the mains supply network, DTMF telephone signal frequencies are used.
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