| 摘要 |
An interface unit for use between a telephone system in which a single-frequency tone is transmitted in both directions when the circuit is on-hook (idle) and a single-channel-per-carrier radio system in which the radio frequency carrier is not transmitted when the circuit is idle. A transmitting portion includes a single-frequency tone detector means responsive to termination or initiation of the tone from the telephone system to turn on the radio frequency carrier. A receiving portion includes a radio frequency carrier detector means operative to switch the telephone system from the output of a local single frequency local oscillator to a voice frequency line from the radio system, and a single frequency detection means to switch the telephone system back to the output of the local single frequency oscillator.
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