US3761908A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Object detection system
Assignee: General Dynamics Corp
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Filing: 1971-12-20
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Granted: 1973-09-25
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Expires: 1991-12-20
Abstract
Abstract An intrusion detection system is described wherein an antenna establishes a sensing field in the area to be secured. The field having at least two different principal frequencies in the VHF band. These frequencies are generated by heterodyning (double sideband modulation) or by frequency modulation. The cyclic variations in the frequency (frequency shift) or the amplitude variations in the generated signals due to an intruder perturbing the sensing field and are detected by monitoring each frequency and determining the frequency differential or amplitude differential therebetween. The frequency or amplitude differential signal is processed to indicate the presence of an intruder, as by producing an alarm output.
Inventors
- 👤 J Gehman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 18:02
CPC Classifications
G; G01; G01V; G01V3/00; G01V3/08; G01V3/10; G01V3/101; G01V3/102
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
185 words
An intrusion detection system which comprises a. an antenna for establishing a sensing field, b. means for generating a carrier signal, c. means for generating a modulating signal, d. means for modulating said carrier signal with said modulating signal to produce signals having first and second different frequencies, e. a tank circuit including an inductor and a capacitor connected between said modulating means and said antenna for applying said signals having said first and second frequencies to said antenna, f. first and second inductors coupled to said tank circuit inductor, g. first circuit means including said first inductor tuned to said first frequency, h. second circuit means including said second inductor tuned to said second frequency, i. detector circuit means connected to said first and second circuit means for detecting variations in the difference between a like parameter of said signals having said first and second different frequencies to which said first and second circuit means are tuned to produce an output signal corresponding to said difference, and j. means Responsive to said output signal for indicating the presence of an output in said field.
Claim 2
Dependent Claim
185 words
An intrusion detection system which comprises a. an antenna for establishing a sensing field, b. means for generating a carrier signal, c. means for generating a modulating signal, d. means for modulating said carrier signal with said modulating signal to produce signals having first and second different frequencies, e. a tank circuit including an inductor and a capacitor connected between said modulating means and said antenna for applying said signals having said first and second frequencies to said antenna, f. first and second inductors coupled to said tank circuit inductor, g. first circuit means including said first inductor tuned to said first frequency, h. second circuit means including said second inductor tuned to said second frequency, i. detector circuit means connected to said first and second circuit means for detecting variations in the difference between a like parameter of said signals having said first and second different frequencies to which said first and second circuit means are tuned to produce an output signal corresponding to said difference, and j. means Responsive to said output signal for indicating the presence of an output in said field.
Claim 3
Dependent Claim
51 words
The invention as set forth in claim 1 wherein said detector circuit means each includes first and second amplitude modulation detectors connected to said first and second circuit means and means responsive to the difference between the outputs of said first and second amplitude modulation detectors for producing said output signal.
Claim 4
Dependent Claim
54 words
The invention as set forth in claim 1 wherein said detector circuit means includes a mixer connected to said first circuit means and to said second circuit means for deriving said first and second frequencies, and a frequency discriminator responsive to variations in frequency of said difference frequency signal for producing said output signal.
Claim 5
Dependent Claim
137 words
An intrusion detection system which comprises a. an antenna for establishing sensing field, b. a variable frequency oscillator producing a carrier signal, c. a square wave generator producing a modulating signal, d. means for applying said modulating signal to said variable frequency oscillator to produce a modulated signal having first and second frequencies as principal components at alternate successive intervals of time corresponding to alternate half cycles of said modulating signal, e. means for applying said signals having said first and second different frequencies to said antenna for exciting said antenna to produce said sensing field, f. means for detecting variations in the difference between a like parameter of said first and second frequencies to produce an output signal, and g. means responsive to said output signal for indicating the presence of an object in said field.
Claim 6
Dependent Claim
137 words
An intrusion detection system which comprises a. an antenna for establishing sensing field, b. a variable frequency oscillator producing a carrier signal, c. a square wave generator producing a modulating signal, d. means for applying said modulating signal to said variable frequency oscillator to produce a modulated signal having first and second frequencies as principal components at alternate successive intervals of time corresponding to alternate half cycles of said modulating signal, e. means for applying said signals having said first and second different frequencies to said antenna for exciting said antenna to produce said sensing field, f. means for detecting variations in the difference between a like parameter of said first and second frequencies to produce an output signal, and g. means responsive to said output signal for indicating the presence of an object in said field.
Claim 7
Dependent Claim
30 words
The invention as set forth in claim 4 wherein said detecting means includes synchronous detectors responsive to said modulated signal and to said modulating signal for producing said output signal.
Claim 8
Dependent Claim
81 words
The invention as set forth in claim 5 wherein said detecting means coupled to said means for applying said signal to said antenna for deriving said modulated signal as varied by objects in said sensing field includes first and second synchronous detectors, means for applying said modulating signal and said modulated signals to different ones of said synchronous detectors in opposite phase relationship, and means responsive to the sum of the outputs of said synchronous detectors for providing said output 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) | 1976-09-24 | 1977-03-26 | 1977-09-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-09-24 | 1981-03-26 | 1981-09-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-09-24 | 1985-03-26 | 1985-09-25 | $7700.00 | Window Closed / Lapsed |