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Early Color Television

RCA Dot Sequential System (US, 1941-49)

RCA's dot sequential system approach to solve the bandwidth limitation was one proposed by Alda Bedford of RCA, the use of "mixed highs." This relied on the limitation of the eye's relative insensitivity to the fine detail of color, the portion of the picture that requires the transmission of higher frequency components. Bedford proposed that these components be separated from the three color signals, mixed, and then added to the GREEN signal. The bandwidth of the red and blue signals could then be reduced substantially. Another addition, the use of a burst (train of 8 cycles of a sine wave) to the color signal provided a solid synchronism between camera source and receiver, and overcame noise which would cause instability. Field tests brought about the change of color to orange-red and blue-green to take advantage of the eye's insensitivity to fine detail in the blue-green region, thereby narrowing the blue-green band.

Red, green and blue color signals are produced continuously and simultaneously. These signals are then sampled in sequence at a rapid rate, nominally 3.6 MHz. The output of the sampling process is a series of pulses, each having an amplitude proportional to the amplitude of the corresponding color signal at that point in the picture. This signal produces a series of tiny (approximately 0.03" wide) colored dots on a tricolor kinescope. These are perceived by the eye as a single color with a hue determined by the relative amplitude of the red, green and blue pulses at that point. Here are RCA press releases about the system.

Here is a 1949 RCA presentation to the FCC about this system courtesy of George Lemaster and a RCA promotional brochure, courtesy of John Tyminski.