CBS Field Sequential System (US, 1940-1953)

This field sequential system displayed red, green, and blue television images in sequences, and depended upon the retentivity of the eye to merge these into a single color picture. If, however, flicker and picture sharpness were to be maintained at the level of monochrome television, a field sequential broadcast signal would require three times the bandwidth of monochrome. A compromise or trade off was reached by increasing the bandwidth from 4 to 5 MHz, number of frames were reduced from 30 to 20 per second, and scanning lines reduced from 525 to 343. For this reason it was incompatible with existing black and white broadcasting.

This was a hybrid system. It used a rotating disk, but it was not a scanning disk; it contained red, green, and blue filters arranged in radial arcs. The "color wheel" spun in front of a conventional electronic scanning tube, presenting it with successive red, green, and blue images. The receiver had a similar color wheel, displaying the successive images to reconstruct the full color image.

The chart below shows how the color bands were scanned and recombined on the CBS system to form all hues, black, and white in the full color picture. (Information and pictures courtesy of Rick Plummer)

CBS arranged demonstrations of their color system for NTSC members and FCC officials on 28 August and 4 September 1940. They were shown beautiful color imagery with 343 lines of resolution on a TV screen 18 centimeters wide, operating at CBS labs in New York City. The audience found it impressive. FCC Chairman Fly was enthusiastic enough to declare: "If we can start television off as a color proposition, instead of a black and white show, it will have a greater acceptance with the public." A magazine article describes the system in April of 1941.

An RCA representative on the NTSC replied that his company was aware of and unimpressed by the CBS system, and called it a "mechanical system". RCA's technology was the leader in the current race to establish TV standards, and the company was not happy at a CBS effort to muddy the waters.

A November, 1941 document from CBS entitled "Progress Report on Color Television", contains photos of early CBS equipment. Life Magazine featured articles on the CBS system in 1941.

Here is a film clip from a 1946 color demonstration by CBS. This clip is from Pete Deksnis's site, where you can find more on it.

Their 1949 Color System was the third field sequential approach to be proposed to the FCC for adoption. They had suggested that their field sequential standards be adopted in 1941 and 1946. At those earlier times, with few black and white receivers in the hands of the public, the adoption of the non-compatible CBS system might have been feasible. In 1950 the FCC approved the CBS system over the RCA compatible approach, mainly because the picture quality was superior. After the adoption of the CBS system, Packard-Bell's president Robert Bell made a presentation to the RTMA critical of the system.

In 1951 CBS began test broadcasting, using a field-sequential system of 405 lines, 144 fields per second, incompatible with the NTSC black-and-white standard. Due to the Korean War, CBS stopped color broadcasting 4 months later. Federal Telephone and Radio Corp. built a UHF transmitter for the CBS system.

A few receivers were manufactured for the CBS system, including one by Sears-Silvertone, and converters were sold to turn a black and white set in color. Some people made their own converters.

CBS also developed an all electronic color TV system which was a projector type having the equivalent of a 22 inch screen.  Three images were produced on the face of the tube and these were combined optically.

For a more detailed history of CBS color, see Bob Cooper's article. Extensive information on early color systems can be found at Ed Reitan's site. Dave Johnson wrote an article about Peter Goldmark, CBS's chief engineer and inventor of the CBS field sequential system.

The museum has a working Gray Research field sequential color monitor and a Converter designed for the CBS system. Click for newspaper and magazine articles about CBS color.

Color camera (1945)