Variable frequency communication system

• US 3,909,722 A
• Filed: 06/22/1973
• Issued: 09/30/1975
• Est. Priority Date: 06/22/1973
• Status: Expired due to Term

• Current Assignee: Victor A. Bennett Jr
• Original Assignee: Victor A. Bennett Jr
• Inventors: Bennett, Victor A. Jr.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Ng, Jin F.
• Application Number:
  US05/372,641
• Time in Patent Office: 830 Days
• Field of Search: 325/22,43,45,55,35,64,105,117,111,131,152,349,364,455,132,145 340/224,171R,177R,27R,208
• US Class Current: 340/539.1
• CPC Class Codes: G08B 25/10 using wireless transmission systems G08B25/009 takes precedence

Abstract

An alarm condition for a predetermined time interval turns a transmitter on that radiates a frequency modulated signal over a substantial portion of the FM band at a predetermined modulating rate that is preferably slightly superaudio outside the usual usable frequencies in the frequency modulating band. A frequency modulation receiver is tuned to a clear channel in the frequency range over which the transmitter frequency is deviated to provide a demodulated signal of frequency at the predetermined sweep rate that is passed by a tone filter to signify the alarm condition. The transmitter may include a low battery indicator signal source that produces a deviation rate different from that produced upon the occurrence of an alarm condition so that a low battery condition may be detected by the receiver.

Claims

1. Variable frequency communicating apparatus comprising, means for radiating a low power frequency modulated signal having a power output of 100 milliwatts maximum, means for deviating the frequency of said signal over a bandwidth than spans a plurality of adjacent FM broadcast channels at a rate at least equal to an audio frequency, and receiving means tuned to a center frequency in the FM band that is clear of standard FM broadcast signals detectable by said receiving means for providing tones representing the modulated signal and said receiving means having means for selectively passing said tones within a predetermined bandwidth for selectively detecting the rate at which said deviation occurs.

2. Variable frequency communicating apparatus in accordance with claim 1 wherein the frequency deviation spans at least ten continuous standard FM broadcast channels.

3. Variable frequency communicating apparatus in accordance with claim 1 wherein said receiving means further comprises step frequency changer means for switching said center frequency between first and second frequencies separated by a frequency difference less than said bandwidth at a rate corresponding to an audio frequency.

4. Variable frequency communicating apparatus in accordance with claim 1 wherein said receiving means further comprises, inverse automatic frequency control for tuning said receiving means to a center frequency in the FM broadcast band that is clear of standard FM broadcast signals for receiving the radiated frequency modulated signal and having means for providing a detected signal having a tone frequency corresponding to the rate at which the frequency modulated signal frequency is deviated, and means for selectively transmitting signals of said tone frequency to indicate an alarm condition in response to the occurrence of said detected signal.

5. Variable frequency communicating apparatus in accordance with claim 4 wherein said receiving means further comprises step frequency changer means for switching said center frequency between first and second frequencies separated by a frequency difference less than said bandwidth at a rate corresponding to an audio frequency.

6. Variable frequency communicating apparatus comprising, means for radiating a low power frequency modulated signal having a power output of 100 milliwatts maximum, means for deviating the frequency of said signal over a bandwidth that spans a plurality of adjacent FM broadcast channels at a rate at least equal to an audio frequency wherein said means for deviating comprises a normally quiescent modulating multivibrator coupled to a frequency-modulated oscillator for deviating the frequency of the latter when said modulating multivibrator is nonquiescent, and further comprising switching means responsive to occurrence of an alarm condition for rendering said modulating multivibrator in a free-running condition to deviate the frequency of said frequency modulated oscillator over said bandwidth at the free-running rate of said modulating multivibrator.

7. Variable frequency communicating apparatus comprising, means for radiating a low power frequency modulated signal having a power output of 100 milliwatts maximum wherein said means for radiating comprises, an oscillator having a voltage-controlled capacitance comprising means for controlling the oscillator frequency, and means for deviating the frequency of said signal over a bandwidth that spans a plurality of adjacent FM broadcast channels at a rate at least equal to an audio frequency, said means for deviating comprising a free-running multivibrator including means for providing a ramp voltage waveform to said voltage controlled capacitance of a frequency that is above 15 kHz, away from 19 kHz and outside the 23-53 kHz subcarrier band whereby the ramp voltage waveform varies the voltage-controlled capacitance and thereby deviates said oscillator frequency.

8. Variable frequency communicating apparatus in accordance with claim 7 and further comprising, receiving means with inverse automatic frequency control for tuning said receiving means to a center frequency in the FM broadcast band that is clear of standard FM broadcast signals for receiving the radiated frequency modulated signal and having means for providing a detected signal having a tone frequency corresponding to the rate at which the frequency modulated signal frequency is deviated, and means for selectively transmitting signals of said tone frequency to indicate an alarm condition in response to the occurrence of said detected signal.

9. Variable frequency communicating apparatus in accordance with claim 8 and further comprising, said receiving means having step frequency changer means for switching said center frequency between first and second frequencies separated by a frequency difference less than said bandwidth at a rate corresponding to an audio frequency.