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u) The origins of carrier multiplexing



Carrier multiplexing allows for the transmission of large numbers of signals over a common line (wire, cable, optical fiber, etc) by shifting them in frequency. The first demonstration of carrier multiplexing was carried out by George O. Squier of the US Army Signal Corps on Sept. 18th, 1910. He multiplexed two analog signals over a single 7-mile telephone circuit. Dr. Frank Jewett, later president of the Bell Telephone Laboratory, indicated that he saw no great commercial value in the idea because of the attenuation suffered by high-frequency signals. The Bell System's engineers, however, proved him wrong and by 1918 they had developed the first commercial such system for AT&T. As it turns out, Jewett had assumed excessively long lines and that led him to a pessimistic assessment. Today, carrier multiplexing and its variants are ubiquitous.



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