Automatic alarm detector

Claim 1

An automatic system for monitoring pulse modulated RF distress signals and for providing an alarm when prescribed signals are received, wherein the improvement comprises: an RF section for receiving RF signals within a prescribed bandwidth, said RF section including electronic means for converting the RF signals into DC pulses, a logic section for receiving said DC pulses, said logic section including a plurality of electronic circuits connected together to provide an output signal in response to the receipt of a selected number of consecutive pulses, having a prescribed length, which are separated by spaces of acceptable duration, said electronic circuits including first electronic means responsive to the start of one of said DC pulses to provide a trigger signal, an electronic cycle counter responsive to said trigger signal to record the beginning of a DC pulse and to provide output signals to energize a first AND gate, said energized AND gate providing a signal to energize an ''''OR'''' gate, an oscillator coupled to respond to signals from said OR gate to provide timed output pulses during the period of said DC pulse, a timer-counter circuit responsive to said sequences of timed pulses to measure the duration of said DC pulse, a plurality of gates coupled to said timer-counter circuit to provide output signals indicative of the status of the DC pulse, and gating meanS responsive to said output signals to provide further signals indicating when a DC pulse is of proper duration and supplying an inhibit signal to the OR gate causing it to turn off the oscillator, said cycle counter responding to succeeding trigger signals to advance its count by one and energize a second AND gate and said OR gate to start a second cycle of checking through said AND gates and said timer-counter circuit.