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Transmission system with improved tone detection

Image Number 6 for United States Patent #5850437.

In a transmission system, a signalling tone is transmitted by a transmitter to a receiver via a transmission channel. In the receiver, a tone detector detects the presence of a signalling tone. In order to improve a reliability of the tone detector, a number of correlating elements which determine a correlation value between an input signal and a reference signal are used. Absolute output signals of the correlating elements are added by an adder to derive a combined correlation signal to be used for detection.

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