US4423519A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Apparatus and method for detecting the onset of a frequency shift keyed signal
Assignee: Unisys Corp
•
Filing: 1982-01-20
•
Granted: 1983-12-27
•
Expires: 2002-01-20
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, demodulated and integrated to produce a useable detector signal. The detector signal is compared with a threshold signal which is generated to discriminate between the FSK signal and other unwanted signals or noise in the communication channel.
Inventors
- 👤 Clarence L. Bennett, Jr.
- 👤 Robert Price
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 15:51
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10; H04L27/14; H04L1/00; H04L1/20; H04L1/206
Claims Analysis
Total Claims: 54
Claim 1
Independent Claim
97 words
The method of detecting the presence in an incoming signal of a frequency shift keyed signal of known shift frequency, key rate, and key period that comprises (a) time delaying the incoming signal by a first time interval; (b) multiplying the incoming signal by the time delayed signal to produce a first product; (c) filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (d) producing a threshold signal in response to the incoming signal; (e) producing a report signal when the first filtered signal exceeds the threshold signal.
Claim 2
Independent Claim
97 words
The method of detecting the presence in an incoming signal of a frequency shift keyed signal of known shift frequency, key rate, and key period that comprises (a) time delaying the incoming signal by a first time interval; (b) multiplying the incoming signal by the time delayed signal to produce a first product; (c) filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (d) producing a threshold signal in response to the incoming signal; (e) producing a report signal when the first filtered signal exceeds the threshold signal.
Claim 3
Dependent Claim
19 words
The method according to claim 1 wherein the first time interval is an odd multiple of the key period.
Claim 4
Dependent Claim
33 words
The method according to claim 1 wherein the step of filtering the first product comprises filtering the first product through a bandpass filter having a pass band centered substantially at the shift frequency.
Claim 5
Dependent Claim
35 words
The method according to claim 1 wherein the step of filtering the first product comprises filtering the first product through a bandpass filter whose pass band is substantially of width equal to the key rate.
Claim 6
Dependent Claim
19 words
The method according to claim 1 that further comprises producing an integrated signal in response to the incoming signal.
Claim 7
Dependent Claim
20 words
The method according to claim 1 that further comprises demodulating the first filtered signal to produce a first demodulated signal.
Claim 8
Dependent Claim
19 words
The method according to claim 6 wherein the demodulating step is performed by envelope detecting the first filtered signal.
Claim 9
Dependent Claim
52 words
The method for detecting a coherent frequency shift keyed signal of a known finite duration, as recited in claim 1, wherein the step of filtering the first product comprises filtering the first product through a bandpass filter whose pass band is a width substantially equal to the reciprocal of the finite duration.
Claim 10
Dependent Claim
36 words
The method for detecting a frequency shift keyed signal of a known finite duration, as recited in claim 1, that further comprises integrating the first filtered signal over an interval substantially equal to the finite duration.
Claim 11
Dependent Claim
75 words
The method according to claim 1 wherein the step of producing a threshold signal is performed by (a) time delaying the incoming signal by a second time interval; (b) multiplying the incoming signal by the second time delayed signal to produce a second product; (c) filtering the second product to pass a second filtered signal of frequency substantially equal to the shift frequency; (d) providing a threshold signal in response to the second filtered signal.
Claim 12
Dependent Claim
22 words
The method according to claim 10 comprising the additional step of time delaying the second filtered signal by a third time interval.
Claim 13
Dependent Claim
29 words
A method for detecting a frequency shift keyed signal of a known finite duration, according to claim 11, wherein the third time interval is greater than the finite duration.
Claim 14
Dependent Claim
19 words
The method according to claim 10 wherein said second time interval is an even multiple of the key period.
Claim 15
Dependent Claim
32 words
The method according to claim 10 wherein the step of filtering the second product comprises filtering the second product through a bandpass filter having a pass band centered at the shift frequency.
Claim 16
Dependent Claim
35 words
The method according to claim 10 wherein the step of filtering the second product comprises filtering the second product through a bandpass filter whose pass band is substantially of width equal to the key rate.
Claim 17
Dependent Claim
19 words
The method according to claim 10 that further comprises producing an integrated signal in response to the incoming signal.
Claim 18
Dependent Claim
14 words
The method according to claim 10 that further comprises demodulating the second filtered signal.
Claim 19
Dependent Claim
24 words
The method according to claim 17 wherein the step of demodulating the second filtered signal is performed by envelope detecting the second filtered signal.
Claim 20
Dependent Claim
35 words
The method for detecting a frequency shift keyed signal of a known finite duration, according to claim 10, that further comprises integrating the second filtered signal over an interval substantially equal to the finite duration.
Claim 21
Dependent Claim
53 words
The method for detecting a coherent frequency shift keyed signal of a known finite duration, according to claim 10, wherein the step of filtering the second product is performed by filtering the second product through a bandpass filter whose pass band is a width substantially equal to the reciprocal of the finite duration.
Claim 22
Dependent Claim
29 words
A method for detecting a frequency shift keyed signal of a known finite duration according to claim 10 wherein the second time interval is greater than the finite duration.
Claim 23
Dependent Claim
83 words
A method for detecting the presence of a frequency shift keyed signal in an incoming signal which includes an intermittent pair of continuous wave signals separated in frequency by the frequency shift, according to claim 1, wherein the step of producing a threshold signal comprises producing a binary threshold signal having a first state when the incoming signal does not include the pair of continuous wave signals, and having a second state when the incoming signal includes the pair of continuous wave signals.
Claim 24
Dependent Claim
33 words
The method according to claim 1 comprising the additional step of comparing the first filtered signal with the threshold signal to produce a comparison signal and performing binary integration on the comparison signal.
Claim 25
Independent Claim
167 words
A method of detecting the presence in an incoming signal of a coded frequency shift keyed signal having a known shift frequency and alternating in a known sequence of successive intervals that comprises (a) sequentially delaying the incoming signal by a plurality of successive time delays to produce a plurality of time delayed signals, including a first delayed signal and a second delayed signal; (b) multiplying the first delayed signal by the second delayed signal to produce a third signal; (c) producing a fourth signal from the plurality of time delayed signals; (d) filtering the third signal to pass a first filtered signal of frequency substantially equal to the shift frequency and filtering the fourth signal to pass a second filtered signal of frequency substantially equal to the shift frequency; (e) combining the first and second filtered signals to produce a detector signal; (f) producing a threshold signal in response to the incoming signal; (g) producing a report signal when the detector signal exceeds the threshold signal.
Claim 26
Independent Claim
167 words
A method of detecting the presence in an incoming signal of a coded frequency shift keyed signal having a known shift frequency and alternating in a known sequence of successive intervals that comprises (a) sequentially delaying the incoming signal by a plurality of successive time delays to produce a plurality of time delayed signals, including a first delayed signal and a second delayed signal; (b) multiplying the first delayed signal by the second delayed signal to produce a third signal; (c) producing a fourth signal from the plurality of time delayed signals; (d) filtering the third signal to pass a first filtered signal of frequency substantially equal to the shift frequency and filtering the fourth signal to pass a second filtered signal of frequency substantially equal to the shift frequency; (e) combining the first and second filtered signals to produce a detector signal; (f) producing a threshold signal in response to the incoming signal; (g) producing a report signal when the detector signal exceeds the threshold signal.
Claim 27
Dependent Claim
22 words
The method according to claim 24 wherein the successive time delays correspond in retrograde seriatim to the known sequence of successive intervals.
Claim 28
Independent Claim
119 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 (a) first means for time delaying the incoming signal by a first time interval and for providing a first time delayed signal; (b) first means for multiplying the incoming signal by the first time delayed signal to produce a first product; (c) first means for filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (d) means for producing a threshold signal in response to the incoming signal; (e) means for producing a report signal when the first filtered signal exceeds the threshold signal.
Claim 29
Independent Claim
119 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 (a) first means for time delaying the incoming signal by a first time interval and for providing a first time delayed signal; (b) first means for multiplying the incoming signal by the first time delayed signal to produce a first product; (c) first means for filtering the first product to pass a first filtered signal of frequency substantially equal to the shift frequency; (d) means for producing a threshold signal in response to the incoming signal; (e) means for producing a report signal when the first filtered signal exceeds the threshold signal.
Claim 30
Dependent Claim
29 words
The apparatus according to claim 26 wherein the first time delaying means is adapted to produce a time delay substantially equal to an odd multiple of the key period.
Claim 31
Dependent Claim
25 words
The apparatus according to claim 26 wherein the first filtering means comprises a bandpass filter having a pass band centered substantially at the shift frequency.
Claim 32
Dependent Claim
27 words
The apparatus according to claim 26 wherein the first filtering means comprises a bandpass filter whose pass band is substantially of width equal to the key rate.
Claim 33
Dependent Claim
22 words
The apparatus according to claim 26 that further comprises first means for producing an integrated signal in response to said incoming signal.
Claim 34
Dependent Claim
23 words
The apparatus according to claim 26 that further comprises first means for demodulating the first filtered signal to produce a first demodulated signal.
Claim 35
Dependent Claim
20 words
The apparatus according to claim 31 wherein the first demodulating means comprises means for envelope detecting the first filtered signal.
Claim 36
Dependent Claim
44 words
An apparatus for detecting a coherent frequency shift keyed signal of a known finite duration, as recited in claim 26 wherein the first filtering means comprises a bandpass filter whose pass band is a width substantially equal to the reciprocal of the finite duration.
Claim 37
Dependent Claim
38 words
An apparatus for detecting a frequency shift keyed signal of a known finite duration, as recited in claim 26 that further comprises means for integrating the first filtered signal over an interval substantially equal to the finite duration.
Claim 38
Dependent Claim
90 words
The apparatus according to claim 26 wherein the means for producing a threshold signal comprises (a) second means for time delaying the incoming signal by a second time interval and for providing a second time delayed signal; (b) second means for multiplying the incoming signal by the second time delayed signal to produce a second product; (c) second means for filtering the second product to pass a second filtered signal of frequency substantially equal to the shift frequency; (d) providing a threshold signal in response to the second filtered signal.
Claim 39
Dependent Claim
22 words
The apparatus according to claim 35 further comprising third means for time delaying the second filtered signal by a third time interval.
Claim 40
Dependent Claim
35 words
An apparatus for detecting a frequency shift keyed signal of a known finite duration, according to claim 36, wherein the third time delaying means is adapted to produce a delay greater than the finite duration.
Claim 41
Dependent Claim
28 words
The apparatus according to claim 35 wherein said second time delaying means is adapted to produce a delay substantially equal to an even multiple of the key period.
Claim 42
Dependent Claim
24 words
The apparatus according to claim 35 wherein the second filtering means comprises a bandpass filter having a pass band centered at the shift frequency.
Claim 43
Dependent Claim
27 words
The apparatus according to claim 35 wherein the second filtering means comprises a bandpass filter whose pass band is substantially of width equal to the key rate.
Claim 44
Dependent Claim
22 words
The apparatus according to claim 35 that further comprises second means for producing an integrated signal in response to said incoming signal.
Claim 45
Dependent Claim
17 words
The apparatus according to claim 35 that further comprises second means for demodulating the second filtered signal.
Claim 46
Dependent Claim
21 words
The apparatus according to claim 42 wherein the second demodulating means comprises second means for envelope detecting the second filtered signal.
Claim 47
Dependent Claim
38 words
An apparatus for detecting a frequency shift keyed signal of a known finite duration, according to claim 35, that further comprises second means for integrating the second filtered signal over an interval substantially equal to the finite duration.
Claim 48
Dependent Claim
43 words
An apparatus for detecting a coherent frequency shift keyed signal of a known finite duration, according to claim 35 wherein the second filtering means comprises a bandpass filter whose pass band is a width substantially equal to the reciprocal of the finite duration.
Claim 49
Dependent Claim
35 words
An apparatus for detecting a frequency shift keyed signal of a known finite duration according to claim 35 wherein the second time delaying means is adapted to produce a delay greater than the finite duration.
Claim 50
Dependent Claim
86 words
An apparatus for detecting the presence of a frequency shift keyed signal in an incoming signal which includes an intermittent pair of continuous wave signals separated in frequency by the frequency shift, according to claim 26 wherein the means for producing a threshold signal comprises a means for producing a binary threshold signal having a first state when the incoming signal does not include the pair of continuous wave signals, and having a second state when the incoming signal includes the pair of continuous wave signals.
Claim 51
Dependent Claim
34 words
The apparatus according to claim 26 further comprising means for comparing the first filtered signal with the threshold signal to produce a comparison signal and means for performing binary integration on the comparison signal.
Claim 52
Independent Claim
179 words
An apparatus for detecting the presence in an incoming signal of a coded frequency shift keyed signal having a known shift frequency and alternating in a known sequence of successive intervals comprising (a) means for sequentially delaying the incoming signal by a plurality of successive time delays to produce a plurality of time delayed signals, including a first delayed signal and a second delayed signal; (b) means for multiplying the first delayed signal by the second delayed signal to produce a third signal; (c) means responsive to the successive time delays for producing a fourth signal; (d) means for filtering the third signal to pass a first filtered signal of frequency substantially equal to the shift frequency and means for filtering the fourth signal to pass a second filtered signal substantially equal to the shift frequency; (e) means for combining the first and second filtered signals to produce a detector signal; (f) means for producing a threshold signal in response to the incoming signal; (g) means for producing a report signal when the detector signal exceeds the threshold signal.
Claim 53
Independent Claim
179 words
An apparatus for detecting the presence in an incoming signal of a coded frequency shift keyed signal having a known shift frequency and alternating in a known sequence of successive intervals comprising (a) means for sequentially delaying the incoming signal by a plurality of successive time delays to produce a plurality of time delayed signals, including a first delayed signal and a second delayed signal; (b) means for multiplying the first delayed signal by the second delayed signal to produce a third signal; (c) means responsive to the successive time delays for producing a fourth signal; (d) means for filtering the third signal to pass a first filtered signal of frequency substantially equal to the shift frequency and means for filtering the fourth signal to pass a second filtered signal substantially equal to the shift frequency; (e) means for combining the first and second filtered signals to produce a detector signal; (f) means for producing a threshold signal in response to the incoming signal; (g) means for producing a report signal when the detector signal exceeds the threshold signal.
Claim 54
Dependent Claim
22 words
The apparatus according to claim 49 wherein the successive time delays correspond in retrograde seriatim to the known sequence of successive intervals.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1986-12-26 | 1987-06-27 | 1987-12-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1990-12-26 | 1991-06-27 | 1991-12-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1994-12-26 | 1995-06-27 | 1995-12-27 | $7700.00 | Window Closed / Lapsed |