Multi-frequency alarm system receiver with interference detection
View Patent ↗An alarm system receiver that is capable of receiving signals transmitted from wireless intrusion detectors at more than one frequency and automatically switching from receiving at one frequency to receiving at a different frequency based on the detection of an interference signal. The alarm system receiver senses a first signal, filters the sensed first signal at a first frequency, demodulates the filtered first signal at the first frequency, and determines if a first interference signal is present in the demodulated first signal for a predetermined time. If the first interference signal is not present in the demodulated first signal, it processes the demodulated first signal as an alarm system signal. If the first interference signal is present in the demodulated signal, the alarm system receiver senses a second signal, filters the sensed second signal at a second frequency, demodulates the filtered second signal at the second frequency, and processes the demodulated second signal as an alarm signal. The alarm system receiver consists of an antenna, more than one filter, more than one local oscillator for providing oscillator signals at the predetermined frequencies, a demodulator for inputting one of the oscillator signals and a corresponding one of the filtered signals to provide a demodulated signal, and an interference detection circuit for inputting the demodulated signal, determining if an interference signal is present in the demodulated signal, and providing an interference detection signal.
1. An alarm system receiver comprising:
a. an antenna for sensing signals,
b. a first filter for filtering said sensed signals at a first frequency to provide a first filtered signal and a second filter for filtering said sensed signals at a second frequency to provide a second filtered signal;
c. a first local oscillator for providing first oscillator signals at said first frequency and a second local oscillator for providing second oscillator signals at said second frequency;
d. a demodulator for inputting one of said first or second oscillator signals and a corresponding one of said first or second filtered signals to provide a demodulated signal;
e. an interference detection circuit for determining if an interference signal is present in said demodulated signal and for providing an interference detection signal;
f. a slicer circuit for generating a quantized demodulated signal from said demodulated signal,
g. a microcomputer for processing said quantized demodulated signal as an alarm signal and for processing said interference detection signal to provide a frequency select signal; and
h. analog switches for selecting, based on said frequency select signal, one of said first and second oscillator signals and one of said first and second filtered signals to be input into said demodulator.
2. The alarm system receiver of claim 1 wherein said first and second frequencies are between 260 MHz and 470 MHz.
3. The alarm system receiver of claim 1 wherein said interference detection circuit determines if an interference signal is greater than a predetermined threshold for a predetermined time.
4. The alarm system receiver of claim 3 wherein said predetermined threshold is [41.66 (μV/m)/MHz]*F-7083.33 μV/m, where F is a predetermined frequency.
5. The alarm system receiver of claim 3 wherein said predetermined time is two seconds.
6. A method of operating an alarm system receiver comprising:
a. sensing signals with an antenna,
b. filtering said sensed signals at a first frequency to provide a first filtered signal and at a second frequency to provide a second filtered signal;
c. providing first oscillator signals at said first frequency with a first local oscillator and second oscillator signals at said second frequency with a second local oscillator;
d. inputting into a demodulator one of said first or second oscillator signals and a corresponding one of said first or second filtered signals to provide a demodulated signal;
e. providing an interference detection signal with an interference detection circuit if an interference signal is present in said demodulated signal;
f. generating with a slicer circuit a quantized demodulated signal from said demodulated signal,
g. processing said quantized demodulated signal as an alarm signal;
h. processing said interference detection signal to provide a frequency select signal; and
i. based on said frequency select signal, selecting with analog switches one of said first and second oscillator signals and one of said first and second filtered signals to be input into said demodulator.
7. The method of claim 6 wherein said first and second frequencies are between 260 MHz and 470 MHz.
8. The method of claim 6 wherein said interference detection circuit determines if an interference signal is greater than a predetermined threshold for a predetermined time.
9. The method of claim 8 wherein said predetermined threshold is [41.66 (μV/m)/MHz]*F-7083.33 μV/m, where F is a predetermined frequency.
10. The method of claim 8 wherein said predetermined time is two seconds.