US3746794A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Modulator-demodulator apparatus for communication of digital data over voise grade telephone lines
Assignee: University of Illinois at Urbana-Champaign
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Filing: 1971-07-07
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Granted: 1973-07-17
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Expires: 1991-07-07
Abstract
Abstract A data modem (modulator-demodulator) apparatus for transmitting and receiving digital data over voice grade telephone lines having a multivibrator, a two station counter providing frequencies fo and f1 with 2/1 ratios, composite signal generator responsive to the fo and f1 signals to provide a pulse train comprising an integral number of cycles of fo and f1, wherein one cycle of f1 is provided for each binary one in the incoming digital data signal and two cycles of fo are provided for each binary zero in the incoming digital data signal, filter means for transforming the pulse train into an approximation of a sine wave for coupling over a voice grade telephone line, means for receiving the sine wave containing information, a limiting amplifier and digital comparator for converting the sine wave back into a digital signal, a two stage counter providing an output zero for each pair of pulses in the digital signal, an integrator-comparator providing an output one level for each single cycle of f1, and means for combining outputs from the integrator-comparator and the two stage counter to provide the reconstructed digital data signal.
Inventors
- 👤 J Stifle
- 👤 M Johnson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 22:34
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
310 words
Modulator-demodulator apparatus for transmitting and receiving digital data over voice grade telephone lines, said apparatus comprising: an oscillator for provid1ng a pulse train with a substantially constant repetition frequency, fx; a frequency divider coupled to said oscillator for providing a first pulse train signal with a repetition frequency, fo, equal to fx/2, and a second pulse train signal with a repetition frequency, f1, equal to fx/4; means for receiving an incoming digital data signal; composite signal generator means responsive to said fo and f1 signals and to said incoming digital data signal for provIding a composite pulse train signal comprising an integral number of cycles of fo and f1; filter means coupled to said composite signal generator means for transforming said composite pulse train signal into a frequency modulated sine wave like waveform having a frequency modulated in accordance with said digital data; means for coupling said frequency modulated sine wave like waveform to said voice grade telephone line; means for receiving said frequency modulated sine wave like waveform from said telephone line; means for reconverting said frequency modulated sine wave like waveform into said composite pulse train signal comprising an integral number of cycles of said higher repetition frequency, fo, and said lower repetition frequency, f1; a counter responsive to said composite pulse train; said counter including means for directly providing at the output thereof a first output signal level in response to each consecutive pair of cycles of said higher repetition frequency, fo; an integrator-comparator responsive to said composite pulse train; said integrator-comparator including means for directly providing at the output thereof a second output signal level in response to each cycle of said lower repetition frequency, f1; and a flip-flop directly coupled to the respective outputs of said counter and said integrator-comparator for receiving said respective outputs therefrom and responding thereto to reconstruct said digital data signal.
Claim 2
Dependent Claim
310 words
Modulator-demodulator apparatus for transmitting and receiving digital data over voice grade telephone lines, said apparatus comprising: an oscillator for provid1ng a pulse train with a substantially constant repetition frequency, fx; a frequency divider coupled to said oscillator for providing a first pulse train signal with a repetition frequency, fo, equal to fx/2, and a second pulse train signal with a repetition frequency, f1, equal to fx/4; means for receiving an incoming digital data signal; composite signal generator means responsive to said fo and f1 signals and to said incoming digital data signal for provIding a composite pulse train signal comprising an integral number of cycles of fo and f1; filter means coupled to said composite signal generator means for transforming said composite pulse train signal into a frequency modulated sine wave like waveform having a frequency modulated in accordance with said digital data; means for coupling said frequency modulated sine wave like waveform to said voice grade telephone line; means for receiving said frequency modulated sine wave like waveform from said telephone line; means for reconverting said frequency modulated sine wave like waveform into said composite pulse train signal comprising an integral number of cycles of said higher repetition frequency, fo, and said lower repetition frequency, f1; a counter responsive to said composite pulse train; said counter including means for directly providing at the output thereof a first output signal level in response to each consecutive pair of cycles of said higher repetition frequency, fo; an integrator-comparator responsive to said composite pulse train; said integrator-comparator including means for directly providing at the output thereof a second output signal level in response to each cycle of said lower repetition frequency, f1; and a flip-flop directly coupled to the respective outputs of said counter and said integrator-comparator for receiving said respective outputs therefrom and responding thereto to reconstruct said digital data signal.
Claim 3
Dependent Claim
19 words
Apparatus as claimed in claim wherein wh1rein said incoming digital data signal comprises binary one and zero data bits.
Claim 4
Dependent Claim
44 words
Apparatus as claimed in claim 2, wherein said composite signal generator means provides one cycle of said frequency, f1, for each binary one in said digital data signal and two cycles of said frequency, fo, for each binary zero in said digital data signal.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-07-16 | 1977-01-15 | 1977-07-17 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-07-16 | 1981-01-15 | 1981-07-17 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-07-16 | 1985-01-15 | 1985-07-17 | $7700.00 | Window Closed / Lapsed |