t only twelve channels. Soon afterward, U.S. entry into World War II interrupted all television progress. The federal government banned manufacture because to conserve resources for the war effort. It was only after the war ended, in 1946, that television broadcasting resumed in earnest. In 1952, the FCC established ultra-high frequency (UHF) television channels, which it numbered 14-83, and extended from 470 to 890 MHz. The FCC also reserved TV channels for non-commercial educational stations, specified mileage separation distances to reduce the potential of interference between TV stations, and made city- by-city television assignments. Ultraviolet Enlarged portion of the visible spectrum Infrared Green Yellow Orange Broadcast range Hertzian waves X-rays Gamma rays Short radio waves long radio Very long waves waves Radar Wave length (meters) 10 12 Frequency (cycles/seconds) Figure 5-5. Frequency Chart: X-rays to Radio Waves (Michel Bayard) Video Communications: The Whole Picture The monochrome image of 1950s TV sets needed frequent adjustment. Viewers had to fiddle with vertical and horizontal hold, twist knobs to juggle light-dark contrast and fuss with the antennae to eliminate ghost-like images and snow. Nevertheless, television achieved overnight acceptance. Market penetration accelerated from 6% of US households in 1949, to 49% in 1953. This was an average growth rate of more than 300% for the first five years of commercial operationAlthough post-war US viewers tolerated black and white (monochrome) TV, they wanted color. It had been available in Europe for years. Americans were not to be outdone. The FCC started exploring ways of adding color to the existing monochrome system and, in 1950, tentatively endorsed what CBS had developed and referred to as a field-sequential system. In this system, a monochrome camera scanned an image, as with black-and- white TV. Unlike monochrome filming however, it placed in front of the lens a color wheel that it divided into transparent RGB sectors (see Figure 5-4). The t