US3746998A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Automatic carrier acquisition system
Assignee: Individual
•
Filing: 1971-12-13
•
Granted: 1973-07-17
•
Expires: 1991-12-13
Abstract
Abstract An automatic carrier acquisition system for a phase-locked loop (PLL) receiver is disclosed. It includes a local oscillator, which sweeps the receiver to tune across the carrier frequency uncertainty range until the carrier crosses the receiver IF reference. Such crossing is detected by an automatic acquisition detector. It receives the IF signal from the receiver as well as the IF reference. It includes a pair of multipliers which multiply the IF signal with the IF reference in phase and in quadrature. The outputs of the multipliers are filtered through bandpass filters and power detected. The output of the power detector has a signal DC component which is optimized with respect to the noise DC level by the selection of the time constants of the filters as a function of the sweep rate of the local oscillator. The power detector output passes through another filter, whose time constant is chosen to optimize the peak of a pulse produced around zero beat with respect to the root-mean-square (RMS) of the noise variations. When the amplitude of this pulse is not less than a selected amplitude, an acquisition trigger at zero beat pulse is produced to stop the sweep and close the PLL, in which the local oscillator serves as the voltage controlled oscillator of the loop.
Inventors
- 👤 J Fletcher
- 👤 R Bunce
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 14:32
CPC Classifications
H; H03; H03L; H03L7/00; H03L7/06; H03L7/08; H03L7/10; H03L7/12
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
269 words
In a communication system receiver of the type including a receiving unit which receives a carrier frequency and a variable frequency from a local oscillator, and which includes a source of reference intermediate frequency definable as an IF reference, said receiving unit providing an IF signal which is a function of the difference between the carrier and local oscillator frequencies, an arrangement for detecting zero beat representing the time when the difference between the carrier and local oscilllator frequencies is substantially equal to said IF reference, the arrangement comprising: a local oscillator for providing a frequency which varies at a preselected sweep rate; a first multiplier for multiplying said IF signal by said IF reference; phase shift means for phase shifting said IF reference by 90*; a second multiplier for multiplying said IF signal by the IF reference shifted by 90* ; first and second filter means for filtering the outputs of said first and second multipliers, respectively; first and second squaring means for squaring the outputs of said first and second filter means, respectively; summing means for providing an output signal which is the sum of the outputs of said first and second squaring means; third filter means for filtering the output signal of said summing means; output means responsive to the output of said third filter means for providing an output signal indicating zero bEat when the amplitude of the output of said third filter means is not less than a preselected amplitude; and means for applying the output signal of said output means indicating zero beat to said local oscillator to terminate the frequency sweep thereof.
Claim 2
Dependent Claim
269 words
In a communication system receiver of the type including a receiving unit which receives a carrier frequency and a variable frequency from a local oscillator, and which includes a source of reference intermediate frequency definable as an IF reference, said receiving unit providing an IF signal which is a function of the difference between the carrier and local oscillator frequencies, an arrangement for detecting zero beat representing the time when the difference between the carrier and local oscilllator frequencies is substantially equal to said IF reference, the arrangement comprising: a local oscillator for providing a frequency which varies at a preselected sweep rate; a first multiplier for multiplying said IF signal by said IF reference; phase shift means for phase shifting said IF reference by 90*; a second multiplier for multiplying said IF signal by the IF reference shifted by 90* ; first and second filter means for filtering the outputs of said first and second multipliers, respectively; first and second squaring means for squaring the outputs of said first and second filter means, respectively; summing means for providing an output signal which is the sum of the outputs of said first and second squaring means; third filter means for filtering the output signal of said summing means; output means responsive to the output of said third filter means for providing an output signal indicating zero bEat when the amplitude of the output of said third filter means is not less than a preselected amplitude; and means for applying the output signal of said output means indicating zero beat to said local oscillator to terminate the frequency sweep thereof.
Claim 3
Dependent Claim
59 words
The arrangement as recited in claim 1 wherin each of said first and second filter means is characterized by a time constant definable as Tau 1 which is a function of the sweep rate of said local oscillator, and said third filter means is characterized by a time constant, definable as Tau 2, which is related to Tau 1.
Claim 4
Dependent Claim
219 words
In a communication system receiver of the type which receives a carrier frequency comprising: a variable frequency local oscillator providing an output frequency which is variable at a preselected sweep rate; a receiving unit, including a source of an intermediate frequency definable as an IF reference and responsive to the output frequency of said oscillator and said carrier frequency for providing an IF signal whose frequency is a function of the difference between the oscillator''s and carrier frequencies; a first multiplier for providing an output as a function of the IF signal and said IF reference; phase shifting means for phase shifting said IF reference by 90*; a second multiplier for providing an output as a function of the IF signal and said IF reference shifted by 90*; first and second filters for filtering the outputs of said first and second multipliers respectively, each of said filters being definable by the transformation 1/1 + Tau 1 S wherein Tau 1 is a time constant which is a function of the sweep rate; power detection means for providing an output which is the sum of the squared outputs of said first and second filters; and output means for providing an output signal whenever the amplitude of the output of said power detection means is not less than a preselected amplitude.
Claim 5
Dependent Claim
219 words
In a communication system receiver of the type which receives a carrier frequency comprising: a variable frequency local oscillator providing an output frequency which is variable at a preselected sweep rate; a receiving unit, including a source of an intermediate frequency definable as an IF reference and responsive to the output frequency of said oscillator and said carrier frequency for providing an IF signal whose frequency is a function of the difference between the oscillator''s and carrier frequencies; a first multiplier for providing an output as a function of the IF signal and said IF reference; phase shifting means for phase shifting said IF reference by 90*; a second multiplier for providing an output as a function of the IF signal and said IF reference shifted by 90*; first and second filters for filtering the outputs of said first and second multipliers respectively, each of said filters being definable by the transformation 1/1 + Tau 1 S wherein Tau 1 is a time constant which is a function of the sweep rate; power detection means for providing an output which is the sum of the squared outputs of said first and second filters; and output means for providing an output signal whenever the amplitude of the output of said power detection means is not less than a preselected amplitude.
Claim 6
Dependent Claim
28 words
The arrangement as recited in claim 3 further including means for applying the output signal of said output means to said oscillator to terminate the frequency sweep thereof.
Claim 7
Dependent Claim
30 words
The arrangement as recited in claim 3 wherein Tau 1 is substantially equal to 1/ Square Root 2 pi f wherein f is the sweep rate in cycle per second.
Claim 8
Dependent Claim
71 words
The arrangement as recited in claim 3 wherein said output means include a third filter to which the output of said power detection means is supplied and comparing means for providing said output signal whenever the amplitude of the output of said third filter is not less than said selected amplitude, said third filter being characterized by the transformation 1/1 + Tau 2 S, wherein Tau 2 is a time constant.
Claim 9
Dependent Claim
32 words
The arrangement as recited in claim 6 wherein the time constant of said third filter is definable as Tau 2 which is in the range of one to four times Tau 1.
Claim 10
Dependent Claim
30 words
The arrangement as recited in claim 7 wherein Tau 1 is substantially equal to 1/ Square Root 2 pi f wherein f is the sweep rate in cycles per second.
Claim 11
Dependent Claim
25 words
The arrangement as recited in claim 8 further including means for terminating the sweep of said oscillator when said output means provide said output signal.
Claim 12
Dependent Claim
17 words
The arrangement as recited in claim 8 wherein Tau 2 is substantially equal to 1.68 Tau 1.
Claim 13
Dependent Claim
25 words
The arrangement as recited in claim 10 further including means for terminating the sweep of said oscillator when said output means provide said output signal.
References Cited (Backward Citations)
US2837646A
Cited
US3358234A
Cited
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 |