Paired signal transmission system utilizing quadrature modulation

Claim 1

A transmission system for two information signals, comprising: transmitting apparatus including: a first source of an input signal having high and low frequencies; a second source of input signal having high and low frequencies; a first amplitude modulator; first filter means connected between said first signal source and one input of said modulator for passing high frequencies above a first predetermined frequency and attenuating low frequencies therebelow; second filter means connected between said first signal source and said first modulator one input for passing low frequencies below said first predetermined frequency and attenuating high frequencies thereabove; a second amplitude modulator; third filter means connected between said second signal source and said first modulator one input for passing low frequencies below a second predetermined frequency and attenuating high frequencies thereabove; fourth filter means connected between said second signal source and one input of said second modulator for passing high frequencies above said second predetermined frequency and attenuating low frequeNcies therebelow; said second predetermined frequency being so selected that modulation utilizing said passed second signal high frequencies produces modulation components excluded from the vicinity of said carrier signal component; a generator of a carrier frequency signal having one terminal connected to another terminal of said first modulator for producing first modulation components including double sidebands of said passed first signal high frequencies, double sidebands of the sum of said passed first and second low frequencies; and a carrier signal component; first phase shifting means connected to second terminal of said carrier generator for providing said carrier signal with a quadrature relationship relative to the phase of said carrier signal in said first modulator; said phase shifting means connected to another terminal of said second modulator for producing second modulation components including quadrature second signal high frequency double sideband components while suppressing said quadrature carrier signal; said quadrature second signal components excluding components lying in the vicinity of said carrier signal component in said first modulation components; circuit means supplying said first modulation components including said carrier signal component and said quadrature second signal modulation components from outputs of said first and second modulators, respectively, to a common point for transmission wherein said quadrature second modulation components unaffect the phase of said carrier signal component in said first modulation components; and receiving apparatus for receiving said first modulation components including said carrier signal component and said quadrature second signal components transmitted from said common point, comprising: fifth filter means for extracting from said received first modulation components a carrier signal equivalent in phase with the phase of said carrier signal generated in said transmitting apparatus; a first amplitude demodulator activated by said received first modulation components and said extracted carrier signal for deriving therefrom an output including said first signal high and low frequencies and said second signal low frequencies; second phase shifting means for providing said extracted carrier signal with a quadrature relationship relative to said extracted carrier signal in said first demodulator; a second amplitude demodulator activated by said quadrature extracted carrier signal and said received quadrature second signal modulation components for deriving therefrom an output including said second signal high frequencies; a first output terminal for receiving thereat said first signal high and low frequencies and said second signal low frequencies from said first demodulator output; sixth filter means having a pass-band for selecting said low frequencies of said first and second input signals from said first demodulator output; and a second output terminal for receiving thereat said first and second signal low frequencies from an output of said sixth filter means and said second signal high frequencies from said second demodulator output.