Projection engineering (Jan-Dec 1931)

DECEMBER, 193 Page 13 A new system of color television By Henri F. Dalpayrat IT is generally believed that the art of television is still in its infancy and just recently emerged from the experimental stage, but this is not wholly true and does not accord with the facts. All the fundamental principles of television were known more than thirty years ago, but due to the lack of certain necessities it was then only possible to speculate on theories which, although sound in principle gave but crude and inefficient results when reduced to practice. The recent improvements made in photoelectric cells, neon tubes, crater tubes, better scanning systems and a better understanding of the principles of electron discharge devices, resulted in the production of several television systems, among which the three best known are: First — the neon plate tube and perforated disc; second — the crater lamp and the lens disc; third — the cathode-ray tube. These systems offered to the public would give interesting performances, but the majority of manufacturers prefer to wait for ultimate developments, especially in new transmission systems which will make possible the reproduction of pictures composed of several hundred lines. When the problem of transmitting such a large number of modulated frequencies over a narrow channel is solved, larger pictures and wider scenes with finer definition of details will be available. Mechanical systems are cumbersome since they give crude results and can only produce small pictures, being limited by the number of holes or lenses. The Kerr cell system is regarded as impractical for home use on account of its high cost of operation and its mechanical complications. The cathode• ray tube is advantageous perhaps only for small pictures and may become expensive when large, clear pictures are desired, as the size of the tube has to be increased in proportion and much more power has to be delivered by larger and more expensive accessories. A television engineer has recently designed a new system of projection Here are described new possibilities in the way of television betterment where the signal modulates a light which is scanned electrically by magnetic fields and projected forward from the device upon a large screen. It is easy to visualize the enormous possibilities of television broadcasting when applied to advertising purposes. A verbal description of an object advertised by radio is always indefinite, as each person forms his own opinion, which is different from that of others, and which will probably be far from the actual picture of the object. With television pictures, the object is better understood, and with colors the picture glows with life-like reality. The interest of the television observer is much increased when the object advertised is seen really as it is. The importance of colors in television is evident, although this fact seems to have been neglected. It is improbable that cathode-ray tubes will ever be designed to reproduce colors. Other systems employing mechanical motions have numerous limitations, and it may be that they will disappear within a year or two. What remains to produce an efficient system able to project either black and white or colored pictures ? Well informed experimenters are convinced that it will be a new sort of electron device operating upon a new principle. Perhaps a system similar to the one described herewith might become popular in the near future as it has all the necessary qualifications without any of the above mentioned limitations. Fig. 1 shows the transmitter of the new system of color television. Fig. 2 is the receiver and Fig. 3 is a new "electronic" commutator, the general principle of which is used in a magnetic light projector. In Fig. 1 (1) is an arc light which throws rays of light through the perforations or lenses of the scanning disc (2) ; upon the subject to be televised (6). The light reflected reaches the photoelectric cells (5) which are mounted on the window (4). This window contains several groups of different cells. One group is mostly sensitive to red light and has color filter screens passing only that color. Another group is more sensitive to blue and has its own color filter. Another group is sensitive to green, and so on. For the purpose of illustration and for the sake of simplicity only the three fundamental or primary colors, blue, red, green are to be used in the present scheme. Each group of photoelectric cells is connected to its contact plate in the "electronic" commutator. This device consists of a tube very much like the cathode-ray tube except that only one set of deflecting plates is used and that the wide end of the tube contains a screen grid which accelerates the speed of the electrons and three separated anodes which consecutively col Elements_ of color television system. r I q 2 Receiver