Baird's Dot-sequential Colour (aka NTSC, PAL) - 1930.

[Stephen]

John Logie Baird described a dot-sequential colour television system in his British Patent GB359,981 filed 30 July 1930. I have posted this patent at http://www.taswegian.com/NBTV/images/GB359981A.pdf . He shows red, green and blue display lights arranged in triplets for each colour pixel in Figure 2 and commutation for sequentially modulating each red, green and blue light within each pixel in Figure 3. See in particular the description of the operation at page 2, column 1, line 45 through column 2, line 64.

Baird's dot-sequential system anticipates the RCA dot sequential system announced 25 August 1949 by nearly twenty years. Instead of the electro-mechanical commutators shown in the Baird patent, RCA used electronic switch commutation thanks to intervening improvements in electronics, but it is otherwise much the same.

Early prototype RCA dot-sequential colour cameras and receivers used this electrical commutation circuitry for colour signal modulation and demodulation. Later, Hazeltine Laboratories recognised that the this time-division multiplex signal sampling actually generated a phase-modulated colour subcarrier signal at the switching frequency, and proposed using phase-modulator and demodulator systems as a simpler means to achieve the same thing.