A Linear AM Stereo System Using Qudature Modulation

Previously proposed systems for AM Stereo are discussed. The new Compatible Phase Multiplex (CPM) AM Stereo system is described. The CPM system is a reduced-angle (300) quadrature system, similar to monaural AM but with the linear addition of reduced-amplitude quadrature sidebands to carry the stereo difference signal. The system also makes possible a change to full quadrature modulation at a future time when envelope detector compatibility may no longer be required. Practical considerations are discussed, including stereo receiver design, compatibility with monaural receivers, and effects of bandpass filtering and noise.