Narrow band synchronized radio communication and alarm system

A narrow band digital communication system for use in connection with signals generated by an existing AC power line comprising:

• first means at a first location for detecting a signal from the power line;
• second means at said first location for generating a first digital code sequence time referenced to as said detected signal;
• third means at said first location for generating a radio signal which is frequency shifted by said first digital code sequence;
• fourth means for detecting the generated radio signals from said third means at a second location;
• frequency discrimination means at said second location for detecting the first digital code sequence from said detected generated radio signal;
• fifth means at said second location for detecting a signal from the power line;
• sixth means at said second location for generating a second digital code sequence at the same frequency as said signal detected by said fifth means from said power line;
• seventh means at said second location for detecting the difference between the second digital code sequence from said second digital code generating means and the first digital code sequence detected by said frequency discriminating means;
• and
• means at said second location connected to said frequency discrimination means and said seventh means whereby a signal is generated when there is no difference in said first and second digital code sequences and an alarm is prevented when there is a difference in said digital code sequences.

A narrow band digital transmitter utilizing signals generated by an existing AC power line, comprising:

• (1) first means for detecting a signal from the power line;
• (2) first synchronizing means responsive to the detected signal for generating a digital clocking frequency:
• (3) first digital code generating means for developing a specific digital pulse sequence in accordance with a preselected code combination, said sequence being generated at the clocking frequency received from said synchronizing means;
• (4) frequency oscillator means for generating a radio signal at a predetermined frequency;
• (5) frequency amplifier means for multiplying and amplifying said radio signal from said frequency oscillator means;
• (6) second means coupled to said frequency amplifier means for transmitting said amplified radio signal;
• (7) frequency divider means for dividing the radio frequency received from said frequency oscillator means;
• (8) comparing means for comparing the divided radio frequency received from said frequency divider means with the digital clocking frequency such that an error signal is generated corresponding to any difference in said signals;
• (9) synchronizing means for combining the error signal and said digital code sequence and applying said combined signal to said frequency oscillator means;
• whereby said radio frequency is synchronized with the digital clocking frequency such that the outgoing transmitted amplified radio signal is frequency shifted in accordance with the digital sequence generated by said digital code generating means.

A narrow band digital receiver using signals generated by a first existing AC power line and a transmitter utilizing signals generated at another location by a second AC power line comprising:

• (1) voltage controlled first oscillator means for generating an output signal;
• (2) third means for detecting the transmitted signals from said transmitter;
• (3) mixing means for mixing the detected transmitted signal and the output of said first oscillator means to provide a mixed signal;
• (4) frequency discrimination means for generating a control voltage which controls the output signal generated by said first oscillator means and for detecting a digital code sequence from said detected transmitted signal;
• (5) fourth means for detecting a signal from the first power line;
• (6) synchronizing means responsive to the signal detected from said power line for generating a digital clocking frequency;
• (7) digital code generating means for generating a specific digital code sequence identical to and in sequence to said detected first digital code sequence;
• (8) amplifying means for detecting the difference in the digital code sequence from said second digital code generating means and from said frequency discriminating means;
• (9) output means responsive to said frequency discrimination means and said amplifying means for creating an output signal;
• whereby when the digital code sequence from said frequency discrimination means and said digital code generating means are identical, an output signal will be generated, and when said sequences are different, said output means will not provide an output signal.

A method of generating a narrow band digital alarm utilizing the frequency generated by existing AC power line, comprising the steps of:

• detecting the frequency of the AC power line at a first location;
• generating a first digital code sequence at the same frequency as the power line;
• generating a radio frequency signal at said first location;
• shifting the frequency of the radio frequency signal by the first digital code sequence generated at said first location and transmitting the frequency shifted radio signal;
• detecting the transmitted frequency shifted signals at a second location;
• detecting the first digital code sequence from said detected frequency shifted signal at a second location;
• detecting the frequency of a power line at second location;
• generating a second digital code sequence identical to and in sequence with said first digital code sequence at a second location;
• detecting the difference between the detected first digital code sequence and in the second digital code sequence generated at the second location;
• creating an alarm at the second location when there is no difference in said first and second digital code sequences, and voiding alarm when there is a difference in said first and second digital code sequences.