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    System for detecting the presence of a received data signal
    3.
    发明授权
    System for detecting the presence of a received data signal 失效
    用于检测接收到的数据信号的存在的系统

    公开(公告)号：US3619785A

    公开(公告)日：1971-11-09

    申请号：US3619785D

    申请日：1969-06-26

    Applicant: BELL TELEPHONE LABOR INC

    Inventor： FARROW CECIL W ,  HOLZMAN LOUIS N

    IPC: H04L1/20 ,  H04H1/10

    CPC classification number: H04L1/20

    Abstract: A system is disclosed for detecting the presence of a received data signal in which a pair of band-pass filters is employed to separate out two pilot tones from the received signal. A mixer is employed to generate a difference frequency which drives a phaselocked oscillator system. The phase-locked oscillator system provides an output signal having the same frequency and phase as the average value of the difference signal. The phase relationship between the difference signal and the output from the phase-locked oscillator system is compared to provide a signal for enabling a data decoding circuit.

    Partial-response signal sampling for half-speed data transmission
    4.
    发明授权
    Partial-response signal sampling for half-speed data transmission 失效
    用于高速数据传输的部分响应信号采样

    公开(公告)号：US3573622A

    公开(公告)日：1971-04-06

    申请号：US3573622D

    申请日：1968-04-23

    Applicant: BELL TELEPHONE LABOR INC

    Inventor： HOLZMAN LOUIS N ,  SHEEHAN JOHN R

    IPC: H03H9/02 ,  H04L25/48 ,  H04L25/497 ,  H04B1/66

    CPC classification number: H04L25/497

    Abstract: Theoretically maximum equivalent binary data transmission rates are obtainable in partial-response channels; i.e., bandlimited channels with filter shaping which disperses the impulse response to individual data inputs over more than one signaling interval. However, the resultant multilevel line signals occasionally give rise to system start-up problems. These problems are eliminated by initial sampling of alternate data input pairs for one particular partial-response format to produce a two-level line signal which preserves transitions occurring at the basic signaling interval. The same technique provides means for signaling at half the design rate without changing channel filters or the basic clock rate.

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