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Abstract

A subscriber data carrier system for simultaneously carrying both base band telephone signals and full duplex digital data transmissions on a single pair of nonloaded telephone wires is disclosed. That is, the system provides for simultaneous conventional telephone signaling and audio communication and full duplex digital data communication between a pair of subscribers, each connected to the same main distribution frame of a central office by a single pair of nonloaded telephone wires. The system includes a modem (21) located at each subscriber's premises. The modems are connected to the subscriber's telephone (23) and digital data terminal (25). The modems include data transmitters (47) and receivers (49) that convert digital data from binary form into FSK form for transmission and from FSK form into binary form upon reception. More specifically, the transmitters include a frequency synthesizer (59) that produces one or the other of two FSK signals (F1 or F2) depending upon the binary nature (0 or 1) of a particular data bit to be transmitted; and, the receivers include frequency detectors (67) that detect two other FSK signals (F3 and F4) and, depending upon the frequency of the detected signal produce a corresponding binary data bit (0 or 1). F1 and F2 are produced in a manner that maintains phase coherency during shifts between F1 and F2 and in a manner such that the waveforms of F1 and F2 are substantially free of harmonics at the frequencies of F3 and F4. The modems also include voice filters (41) that prevent the FSK data signals from reaching the subscribers telephones. The system also includes a repeater (33) located at the central office that bidirectionally converts transmitted FSK signals (i.e., F1 and F2 signals) into receivable FSK signals (i.e., F3 and F4 signals). The repeater (33) also includes voice frequency filters (101,103) that connect the main distribution frame telephone lines to the central office line switching equipment in a manner that prevents the FSK signals from reaching that equipment.

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First Claim