| 摘要 |
An automatic disconnect device with a protected ringer for providing a secure telephone system, the device being interposed between the telephone company outlet and a modified telephone set. The device generates its own audible tone burst only when a standard ring signal is generated by the telephone company and is designed so that no ambient sound can be transmitted back to the telephone outlet. An on-hook/off-hook detector is incorporated in the device to determine when the handset has been lifted off-hook. If off-hook, the telephone operates normally. In the on-hook status, or position, the telephone is automatically disconnected from the telephone outlet at all times. A visual indication is provided when the telephone is on-hook. The incoming telephone company lines from the outlet are conditioned by filters within the device such that the device is not affected by signals other than normal telephone signals. The conditioning filters also prevent spurious signals picked up by the device or telephone from being passed back to the telephone company lines. In essence, only audio-band signals can pass either way through the device when the telephone set is in the off-hook status, or condition.
|
