US4485448A
Expired / Lapsed
US
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Apparatus and method for detecting the onset of a frequency shift keyed signal
Assignee: Unisys Corp
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Filing: 1982-02-26
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Granted: 1984-11-27
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Expires: 2002-02-26
Abstract
Abstract An incoming signal is tested for the presence or onset of a frequency shift keyed (FSK) signal which alternates at a known rate between two unknown frequencies separated by a known frequency shift. The incoming signal is time delayed an odd multiple of the keying period and the delayed signal is multiplied by the incoming signal to produce sum and difference frequencies when the FSK signal is present. The difference frequency is selected by filtration and multiplied by a time delayed version of itself to produce a steady phase signal. The steady phase signal is extracted by filtration, demodulated and integrated to produce a useable detector signal for comparison with a threshold level.
Inventors
- 👤 Richard R. Kurth
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 05:17
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/14
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
241 words
An apparatus for detecting the presence in an incoming signal of a frequency-shift-keyed signal of known shift frequency, key rate, and key period that comprises means for dividing the incoming signal to produce two identical incoming signals; first means for time delaying one of the identical incoming signals by a first time interval and for providing a first time delayed signal; first means for multiplying the other identical incoming signal by the first time delayed signal to produce a first product; first means for filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; dividing the first filtered signal to produce two identical first filtered signals; second means for time delaying one of the identical first filtered signals by a second time interval to produce a second time delayed signal; second means for multiplying the other identical first filtered signal by the second time delayed signal to produce a second product; second means for filtering the second product to pass a second filtered signal of frequency substantially equal to twice the shift frequency; means for producing a threshold signal for comparison with the second filtered signal; means for providing a report signal indicating the presence of the frequency-shift-keyed signal when the second filtered signal exceeds the threshold signal; and means for producing no report signal indicating the absence of the frequency-shift-keyed signal when the second filtered signal does not exceed the threshold signal.
Claim 2
Independent Claim
241 words
An apparatus for detecting the presence in an incoming signal of a frequency-shift-keyed signal of known shift frequency, key rate, and key period that comprises means for dividing the incoming signal to produce two identical incoming signals; first means for time delaying one of the identical incoming signals by a first time interval and for providing a first time delayed signal; first means for multiplying the other identical incoming signal by the first time delayed signal to produce a first product; first means for filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; dividing the first filtered signal to produce two identical first filtered signals; second means for time delaying one of the identical first filtered signals by a second time interval to produce a second time delayed signal; second means for multiplying the other identical first filtered signal by the second time delayed signal to produce a second product; second means for filtering the second product to pass a second filtered signal of frequency substantially equal to twice the shift frequency; means for producing a threshold signal for comparison with the second filtered signal; means for providing a report signal indicating the presence of the frequency-shift-keyed signal when the second filtered signal exceeds the threshold signal; and means for producing no report signal indicating the absence of the frequency-shift-keyed signal when the second filtered signal does not exceed the threshold signal.
Claim 3
Dependent Claim
29 words
The apparatus according to claim 1 wherein the first time delaying means is adapted to produce a time delay substantially equal to an odd multiple of the key period.
Claim 4
Dependent Claim
29 words
The apparatus according to claim 1 wherein the second time delaying means is adapted to produce a time delay substantially equal to an odd multiple of the key period.
Claim 5
Dependent Claim
24 words
The apparatus according to claim 1 wherein the first filtering means comprises a bandpass filter having a passband centered at substantially the shift frequency.
Claim 6
Dependent Claim
25 words
The apparatus according to claim 1 wherein the second filtering means comprises a bandpass filter having a passband centered substantially at twice the shaft frequency.
Claim 7
Dependent Claim
26 words
The apparatus according to claim 1 wherein the first filtering means comprises a bandpas filter whose passband is substantially of width equal to the key rate.
Claim 8
Dependent Claim
47 words
An apparatus for detecting a frequency-shift-keyed signal as recited in claim 1, wherein the frequency-shift-keyed signal additional is of known finite duration and the second filtering means comprises a bandpass filter whose passband is of a width not less than the reciprocal of the known finite duration.
Claim 9
Dependent Claim
43 words
The apparatus according to claim 1 that further comprises means for demodulating the second filtered signal to produce a logical high signal if the frequency shift keyed signal is present and a logical low signal if the frequency shift keyed signal is absent.
Claim 10
Dependent Claim
19 words
The apparatus according to claim 8 wherein the demodulating means comprises means for envelope detecting the second filtered signal.
Claim 11
Dependent Claim
49 words
An apparatus for detecting a frequency shift keyed signal as recited in claim 1, wherein the frequency shift keyed signal additionally is of a known finite duration and the apparatus further comprises means for integrating the second filtered signal over an interal not less than the known finite duration.
Claim 12
Dependent Claim
27 words
The apparatus according to claim 1 wherein the means for producing a threshold signal comprises means for producing a threshold signal in response to the incoming signal.
Claim 13
Independent Claim
222 words
The method of detecting the presence of an incoming signal of a frequency shift keyed signal of known shift frequency, key rate, and key period that comprises (a) dividing the incoming signal to produce two identical incoming signals, (b) time delaying one of the identical incoming signals by a first time interval to produce a first delayed signal; (c) multiplying the other identical incoming signal by the first delayed signal to produce a first product; (d) filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (e) dividing the first filtered signal to produce two identical first filtered signals, (f) time delaying one of the identical first filtered signals by a second time interval to produce a second delayed signal; (g) multiplying the other identical first filtered signal by the second delayed signal to produce a second product; (h) filtering the second product to pass a second filtered signal of frequency substantially equal to twice the shift frequency; (i) producing a threshold signal for comparison with the second filtered signal; (j) producing a report signal indicating the presence of the frequency-shift-keyed signal when the second filtered signal exceeds the threshold signal; (k) producing no report signal indicating the absence of the frequency-shift-keyed signal when the second filtered signal does not exceed the threshold signal.
Claim 14
Independent Claim
222 words
The method of detecting the presence of an incoming signal of a frequency shift keyed signal of known shift frequency, key rate, and key period that comprises (a) dividing the incoming signal to produce two identical incoming signals, (b) time delaying one of the identical incoming signals by a first time interval to produce a first delayed signal; (c) multiplying the other identical incoming signal by the first delayed signal to produce a first product; (d) filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (e) dividing the first filtered signal to produce two identical first filtered signals, (f) time delaying one of the identical first filtered signals by a second time interval to produce a second delayed signal; (g) multiplying the other identical first filtered signal by the second delayed signal to produce a second product; (h) filtering the second product to pass a second filtered signal of frequency substantially equal to twice the shift frequency; (i) producing a threshold signal for comparison with the second filtered signal; (j) producing a report signal indicating the presence of the frequency-shift-keyed signal when the second filtered signal exceeds the threshold signal; (k) producing no report signal indicating the absence of the frequency-shift-keyed signal when the second filtered signal does not exceed the threshold signal.
Claim 15
Dependent Claim
19 words
The method according to claim 12 wherein the first time interval is an odd multiple of the key period.
Claim 16
Dependent Claim
19 words
The method according to claim 12 wherein the second time interval is an odd multiple of the key period.
Claim 17
Dependent Claim
32 words
The method according to claim 12 wherein the step of filtering the first product comprises filtering the first product through a bandpass filter having a passband centered substantially at the shift frequency.
Claim 18
Dependent Claim
33 words
The method according to claim 12 wherein the step of filtering the second product comprises filtering the second product through a bandpass filter having a passband centered substantially at twice the shift frequency.
Claim 19
Dependent Claim
37 words
The method according to claim 12 that further comprises demodulating the second filtered signal to produce a logical high signal if the frequency-shift-keyed signal is present and a logical low signal if the frequency-shift-keyed signal is absent.
Claim 20
Dependent Claim
19 words
The method according to claim 17 wherein the demodulating step is performed by envelope detecting the second filtered signal.
Claim 21
Dependent Claim
34 words
The method according to claim 12 wherein the step of filtering the first product comprises filtering the first product through a bandpass filter whose passband is substantially of width equal to the key rate.
Claim 22
Dependent Claim
56 words
The method for detecting a frequency-shift-keyed signal as recited in claim 12, wherein the frequency-shift-keyed signal additionally is of a known finite duration and wherein the step of filtering the second product comprises filtering the second product through a bandpass filter whose passband is a width not less than the reciprocal of the known finite duration.
Claim 23
Dependent Claim
42 words
The method for detecting a frequency-shift-keyed signal as recited in claim 12, wherein the frequency-shift-keyed signal additionally is of a known duration and the method further comprises integrating the second filtered signal over an interval not less than the known finite duration.
Claim 24
Dependent Claim
27 words
The method according to claim 12 wherein the step of producing a threshold signal is performed by producing a theshold signal in response to the incoming 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) | 1987-11-27 | 1988-05-28 | 1988-11-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-11-27 | 1992-05-28 | 1992-11-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-11-27 | 1996-05-28 | 1996-11-27 | $7700.00 | Window Closed / Lapsed |