Importance

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Abstract

This disclosure concerns a system for digitally detecting one or more of a plurality of fixed frequencies in an analog signal according to a correlation method, the fixed frequencies occurring in a first group and in a second group wherein a third harmonic of one or more frequencies of the first group is equal or almost equal to a frequency of the second group. Each of the frequencies of the first group are represented by a sequence of six equidistant pulses per period, which pulses have the values +1, +1, 0, -1, -1 and 0, respectively; and the frequencies of the second group are represented by a sequence of two equidistant pulses per period, which pulses have the values +1 and -1, respectively. All these reference pulses can be stored in a reference memory (5) which is read out at a frequency whose value is equal to the product of the number of memory places in the reference memory, and the frequency which is the highest common factor of the frequencies to be detected.

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First Claim