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Automatic change-over notification for a receiver

Image Number 2 for United States Patent #3944930.

Circuits for use with a receiver which notify the operator of a receiving station by means of an audio tone when an opposite station is calling or has ceased transmission. The transition of an opposite station from its transmitting to receiving state or vice versa is detected and a specific change-over sound based upon the detector output is introduced into the principal station's receiver audio amplifier circuits.

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