American television directory (1946)

PROGRESS IN COLOR TELEVISION When will color television be available to the public? If field tests, which are already under way, prove successful, 1946 may provide an important answer! _ By PETER G. GOLDMARK Director, Engineering Research and Development Department Columbia Broadcasting System, Inc HISTORY OF COLOR TELEVISION Color television was demonstrated for the first time in July, 1928, by John L. Baird in England. Both at the transmitter and at the receiver, a three-spiral scanning disk was employed. Each of these spirals con¬ sisted of a succession of holes which were covered with red, green, or blue filters, which scanned the picture completely in the three primary colors. At the transmitter, photocells were employed, while at the re¬ ceiver, two gas-discharge tubes controlled by a commutator were used. One of the tubes was filled with neon and acted on the red spiral, while the other tube, filled with a mixture of helium and mercury vapor, appeared through the blue and green spirals. The transmission employed a bandwidth of the order of 10 kilocycles and the pictures corresponded to a number of lines somewhere between 20 and 30 per frame. In July, 1929, Bell Telephone Laboratories, New York, demonstrated a three-color television system employing three independent channels. The live-pickup equipment consisted of three banks of cells with the three primary-color responses. A flying spot scanned the object and a scanning disk served on the receiving end to reconstitute the image. Three discharge tubes furnishing red, green, and blue light and super¬ imposed by mirrors behind the scanning disk served as the light source. Bell Laboratories employed a three-channel system which occupies three times the frequency spectrum over the corresponding black-andwhite picture and requires three times the facilities. Baird, similarly requiring three times the frequency space, employed rotating filters and was thus first to demonstrate the sequential, additive method of color. Early in 1938, John L. Baird demonstrated in England a 9 x 12-foot 120-line color-television picture using sixfold interlacing, employing a flying spot, mirror drum and rotating filters at the transmitter. At the receiving end also a mirror drum was employed, rotating at the rate of 6000 revolutions per minute and using a Kerr cell as modulator in conjunction with rotating color-filter slots. In July, 1939, a demonstration with similar transmitting equipment was reported by Bell Telephone engineers. At the receiver was a projec¬ tion cathode-ray tube combined with a rotating color filter. This was a two-color system using orange and blue-green filters alternately. The color-picture frequency was 16 2/3 per second employing 102 lines. On August 28, 1940, a three-color, high-definition system employing electronic scanning both at the transmitter and at the receiver was broadcast for the first time over CBS Station W2XAB in New York. The subject of transmission was motion-picture color film. Soon after, live pickup employing the same trichromatic system was demonstrated. Beginning on June 1, 1941, daily color transmissions over WCBW inaugurated a field-test period for the purpose of determining the prac¬ ticability of color television. Color drums were used at the receiver as well as at the transmitter instead of color filters. A short cathode-ray tube was placed within this drum which rotated at about half the speed usually possible with a disk. In mid-1944, CBS received FCC permission to construct and operate an ultra-high frequency color television transmitter. It is scheduled for completion and tests by the end of 1945. On October 10, 1945, on labora¬ tory test equipment CBS engineers successfully demonstrated ultra-high frequency broadcasting of clear, ghost-free color pictures on a 10-Mc video band. Although nominally 525-line pictures, each picture contained ‘•1575 imperceptible lines of beautifully detailed color.” We experimented successfully with color television before the war — in fact it was broadcast from our color trans¬ mitter on top of the Chrysler Tower in the center of New York and was re¬ ceived at many locations within a 30mile radius. However, the amount of detail in the picture was not quite sufficient to meet our standards. In order to provide the necessary ex¬ tra detail in the picture, our color sys¬ tem was transferred into the so-called ultra-high frequency region. This is that part of the radio spectrum which is between 300 and 1000 megacycles. This new space in the ether became usable as a result of war research. Whereas, before the war television pictures had to be contained within a bandwidth of 4 megacycles, the new system utilizes 10 megacycles. Government Encouragement With regard to our early contention as to the usability of the new ultrahigh frequencies for color television, it can be stated now that one of the first and most encouraging endorsements came from a group of United States Government experts representing the State Department, the Federal Com¬ munications Commission, the Army and the Navy. Finally, permission for CBS to oper¬ ate a color television station in New York City in these ultra-high frequen¬ cies was granted by the Federal Com¬ munications Commission in mid-1944, and installation of the new transmitter in the spire of the Chrysler Building is scheduled for this year (1945). Addi¬ tional CBS applications are now on file with the Federal Communications Com¬ mission for licenses to operate ultrahigh frequency color television stations in several other cities including Chicago and Los Angeles. Incidentally, the new ultra-high fre¬ quency color television system will also provide black and white pictures, with more than twice as much picture detail as the prewar system. The ultra-high frequency band, which has now been set aside by the Govern¬ ment for experimentation with this new system of television, extends from 480 to 920 megacycles. This furnishes 29 television channels, as compared with ( Continued on page 114) 32