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US 4,302,817 AGranted
Digital Pseudo continuous tone detector
AssigneeMotorola, Inc.
InventorGerald P. Labedz
Life of this patent
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Abstract
Method and apparatus for sampling input signals of different frequencies and providing a detect signal when the input frequency has a predetermined value suitable for use as a tone decoder for continuous tone controlled squelch systems. The method utilizes digital pseudo continuous correlation tone detection, and includes sample matrix limiting to provide rapid reverse burst turnoff, as well as background detection to avoid adjacent channel reverse burst turnoff falsing.
Claims8
A method of processing an input signal to detect at least one desired tone of a plurality of tones, comprising the steps of:
- (a) digitizing the input signal to generate samples of the input signal at a predetermined rate;
- (b) assigning each sample to a phase subregion of a reference waveform where the reference waveform has the frequency of the desired tone;
- (c) summing the sample values for each phase subregion for sequential time intervals to obtain a phase subregion subtotal for each time interval;
- (d) correlating, at the end of each time interval, for a number of the latest time intervals, the phase subregion subtotals against at least one local reference waveform so as to obtain a total correlation value for each local reference waveform, said total correlation value being a total summation of the products of the sum over a number of the latest time intervals of the subtotals of each phase subregion multiplied by the amplitude of a corresponding phase subregion of the local reference waveform;
- (e) processing the total correlation values at the end of each time interval to obtain a sum of the absolute values of the total correlation values;
- (f) comparing at the end of each time interval the sum of the absolute values of the total correlation values to a first threshold in generating a detection indication signal in response to said sum exceeding said first threshold.
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