US3619785A
Expired / Lapsed
US
⏱️ 0.0 years remaining
System for detecting the presence of a received data signal
Assignee: AT&T Inc
•
Filing: 1969-06-26
•
Granted: 1971-11-09
•
Expires: 1989-06-26
Abstract
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.
Inventors
- 👤 Cecil W Farrow
- 👤 Louis N Holzman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 04:10
CPC Classifications
H; H04; H04L; H04L1/00; H04L1/20
Claims Analysis
Total Claims: 2
Claim 1
Independent Claim
113 words
In a data receiver for receiving a modulated data signal including two accompanying pilot tones related by a fixed difference frequency, means for enabling said receiver in the presence of a valid message signal comprising means for detecting the differeNce frequency between said pilot tones, a phase locked oscillator system for providing a phase locked signal coherent in frequency and phase with said difference frequency, said phase locked oscillator system having a response time long compared to the period of said difference frequency, and means responsive to the occurrence of a constant phase relationship between said phase locked signal and the difference frequency wave from said detecting means for unclamping said data receiver.
Claim 2
Dependent Claim
113 words
In a data receiver for receiving a modulated data signal including two accompanying pilot tones related by a fixed difference frequency, means for enabling said receiver in the presence of a valid message signal comprising means for detecting the differeNce frequency between said pilot tones, a phase locked oscillator system for providing a phase locked signal coherent in frequency and phase with said difference frequency, said phase locked oscillator system having a response time long compared to the period of said difference frequency, and means responsive to the occurrence of a constant phase relationship between said phase locked signal and the difference frequency wave from said detecting means for unclamping said data receiver.
References Cited (Backward Citations)
US3183509A
Cited
US3181122A
Cited
US3320535A
Cited
US3450842A
Cited
US3445593A
Cited
US3434056A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-11-08 | 1975-05-10 | 1975-11-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-11-08 | 1979-05-10 | 1979-11-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-11-08 | 1983-05-10 | 1983-11-09 | $7700.00 | Window Closed / Lapsed |