| 摘要 |
A communication circuit (8) carries at least one signal (10, 12, 14, 16, 18) including synchronizing intervals (122) by which output of the signal (10, 12, 14, 16, 18) by first apparatus (52, 54) coupled to the communication circuit (8) is to be synchronized. A modulator (120) is provided for selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals. Another communication circuit carries at least a first signal including frequencies in at least a first frequency band (for example, < 5KHz). A detector is provided for transporting along the circuit (8) for determining whether the first signal is escaping from the circuit (8). The detector is adapted for receiving the first signal, detecting whether a received signal includes frequencies in the first frequency band, and producing an indication that the received signal includes frequencies in the first frequency band. |
