Importance

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Abstract

First and second carrier signals, distinguishable by phase, are respectively applied to infrared and red energy emitters. A detector receives the sum of the energy after modulation at the infrared and red wavelengths. The signal received by the detector is then demultiplexed into its original first and second components, thereby allowing determining of both the infrared and red modulation components. The first and second carrier signals may comprise time-varying periodic signals with identical frequency and frequency spectra, such as a pair of sine waves which are indistinguishable except by phase and amplitude. A 90.degree. phase difference is preferred, but any phase other than 0 or an integer multiple of 180.degree. is workable. A carrier frequency which avoids excessive interference from ambient light is preferred.

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First Claim