Tone receiver for digital data communication systems
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United States of America Patent
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-
Jan 7, 1986
Grant Date -
N/A
app pub date -
Jun 13, 1983
filing date -
Jun 25, 1982
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A device for detecting the presence of an alarm tone of a given frequency within a received signal carrying digital data in addition to said tone. The receiver comprises an analog-to-digital converter (42) the output of which is applied to a first recursive bandpass filter centered at the frequency of the alarm tone and the feedback loop of which includes a limiter. In addition, an input feedforward loop is provided for adding (at 58) the output signal from the converter (42), as multiplied by a coefficient .gamma., to the output signal from the limiter. The output signal from the adder (58) is hard limited (at 44), then passed through a second bandpass filter. The energy of the signal obtained at the output of said second filter is then measured to provide indication of a tone's being received when said energy exceeds a predetermined threshold.
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