Abstract This invention relates to a method for increasing the range of detectability of an emergency locator transmitter beacon, and for conserving transmitter power of the emergency locator transmitter, and to a transmitter and receiver for carrying out the method. In accordance with the invention, the carrier of the transmitter is amplitude modulated with a rectangular waveform whose frequency is a precise submultiple of the carrier frequency. A receiver for the system cross-correlates a received input with a reference signal which is a replica of the modulating waveform. The cross-correlator output indicates whether the received signal is identical to the reference signal, i.e., was transmitted by the transmitter. The reason for making the modulating signal a precise submultiple of the carrier frequency is that, for a correlator to work, the frequency of the correlated waves must be precise. As the carrier frequency of the transmitter is crystal controlled, it is most convenient to take off a submultiple of this frequency to control the modulator precisely. With a system in accordance with the invention, the signal to noise ratio is enhanced to thereby increase the range of detectability. At the same time, the transmitter is turned off cyclically so that transmitter power is conserved.
A method for increasing the range of an emergency locator radio transmitter beacon and for conserving transmitter power of the transmitter; said method comprising; amplitude modulating a carrier waveform, having a frequency which is accurately controlled by a crystal oscillator, of the transmitter with a modulating rectangular waveform at a modulating frequency which is a precise submultiple of the accurately controlled carrier waveform frequency; transmitting the modulated waveform by radio waves; receiving said transmitted signal in a receiver means; demodulating said received signal; and cross-correlating said demodulated signal with the output of a reference signal source in said receiver means to thereby determine whether said demodulated signal is identical with said output, of said reference signal source; providing an indication signal when said demodulated signal is identical with said output of said reference signal source; characterized in that the transmitter is cyclically turned on and off to preserve power.
Claim 2
Independent Claim
149 words
A method for increasing the range of an emergency locator radio transmitter beacon and for conserving transmitter power of the transmitter; said method comprising; amplitude modulating a carrier waveform, having a frequency which is accurately controlled by a crystal oscillator, of the transmitter with a modulating rectangular waveform at a modulating frequency which is a precise submultiple of the accurately controlled carrier waveform frequency; transmitting the modulated waveform by radio waves; receiving said transmitted signal in a receiver means; demodulating said received signal; and cross-correlating said demodulated signal with the output of a reference signal source in said receiver means to thereby determine whether said demodulated signal is identical with said output, of said reference signal source; providing an indication signal when said demodulated signal is identical with said output of said reference signal source; characterized in that the transmitter is cyclically turned on and off to preserve power.