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Cordless telephone

Image Number 4 for United States Patent #4053717.

A cordless telephone including a Touch-tone signal generator module including ten buttons for initiating the generation of telephone switching signals representing ten numeric characters and two additional buttons; one of which is used for switching the cordless telephone into and out of a standby mode of operation in which a ring signal may be received and detected, and the other of which is used for providing off-hook and on-hook switching functions.The telephone lines are seized in response to a discrete control signal transmitted from the cordless telephone, which discrete control signal has a low freqency below an audio frequency band within which audio signals and switching signals transmitted from the cordless telephone are passed onto the telephone lines. These signals are transmitted by frequency modulation.The discrete control signal is summed with signals within the audio frequency band to provide a composite signal and an RF carrier signal is frequency modulated with the composite signal. Intermodulation between the discrete control signal and the audio and switching signals is prevented by providing a linear frequency deviation in response to amplitude variations in the composite signal.

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