International projectionist (Jan-Dec 1939)

impossible to tune them above a certain critical frequency and their high interelectrode capacities make it difficult to load them properly and still preserve the desired band pass characteristics. Thus with tubes of the present types, it is not yet possible to reach the desired power level; and the condition will become more serious as more of the still higher frequency channels are used for television. However, it is reasonable to expect that the ingenuity of tube designers will overcome this difficulty in the next few years. In the meantime, the condition can still be corrected by increasing the height of the transmitting antenna, and especially of the receiving antenna. It requires 12.9 kilowatts of transmitted power to generate a signal of one millivolt in a half-wave dipole 4 meters above the ground at the horizon. This value is independent both of the carrier frequency and of the height of the transmitting antenna. The latter result is very surprising. It indicates that as the antenna height is increased, the same power still suffices to reach the horizon — the increased distance being just compensated by the increased antenna height. Another problem of considerable importance in the adequate coverage of the line-of-sight area is the elimination of multiple reception or echoes. This problem is of practically no importance in sound broadcasting. To get a clear idea of the problem, suppose that in addition to the direct ray travelling from the transmitting to the receiving antennae there is also a ray which reaches the receiving antenna by way of reflection from a large building. This reflected ray will have travelled a greater distance than the direct ray before reaching the receiver. The picture Academy Report on Television Progress REFLECTING the view of West Coast studio technicians anent present status of television is the third annual report of the Research Council of the Academy of Motion Picture Arts & Sciences, a summary of which is appended hereto. England led in putting television on a public service basis, inaugurating regular transmission on Nov. 2, 1936. Has made notable technical progress and in quantity and quality of entertainment, but these advances have not been reflected commercially. Present receiver sales are two sound-only sets to one visual set (some of which include sound). Peak of 4,000 television receivers now indicated for television service area, in which are 10 million people. Public interest has been sustained, with probable extension of coverage promising much wider potential market. Unflagging interest undoubtedly due to visual broadcasts of sporting and ceremonial events, including the Derby, prize fights, tennis matches, boat races, soccer games, etc. Quality of televised image is nowhere near that of 35 mm. film projection, but has reached stage where it can add entertainment value to film houses. Re which it carries will therefore be retarded in time, and it will consequently cause a similar but slightly displaced picture to appear next to the desired picture. This is a very annoying effect, and great effort must be made to avoid it. This effect is illustrated in Fig. 11. A path difference of 127 feet will cause an echo displacement of one picture element. This is enough to detract from the quality of the picture. The elimination or reduction of echoes is a complicated problem. In metropolitan areas, due to the presence (Continued on page 24) FIGURE 4. The effect of multiple-path transmission or reflection upon the received image ceiver sets range in price from $144 to $756, depending upon image size. Programs broadcast average two hours daily, three hours on Saturdays, and one and one-half hours on Sunday. Present standard of 405 lines, 50 frames per second, will not be changed until end of 1940, thus dispelling fears of receiver obsolescence until then. Mobile pick-up unit provided, in addition to cable network in desirable sections of London. Coaxial cable laid between London and Birmingham, to be extended shortly to Manchester, although primarily for telephone purposes, may eventually be used for television. Television transmitter has useful range of 50 miles at present. • Developments in Germany Experimental station in Berlin utilizes same power as London transmitter, 17 kw, with definition of 441 lines and frame frequency of 50 per second. Two other transmitters are planned. A picture 12 by 10 feet has been shown in a theatre. There are reports of a 700-line image. Cathode-ray tubes up to 26" diameter have been built. Cost of receivers is said to range between $175 and $1,000, with $320 as an average. • France Relatively Inactive Eiffel Tower transmitter, rated at 25 kw, more powerful than Berlin or London; its signals have been viewed 180 miles distant. Station transmits daily for 2*A hours. There are reports of a 12 by 9 foot theatre demonstration, with quality approaching 16 mm. projection. No information on receivers or extent of programs. • Developments in the U. S. RCA-NBC experimenal transmissions from Empire State Tower (N.Y. City) have continued since July, 1936. System uses 441 lines, 60 frames per second. Home television now regarded as "technically feasible". RCA promises limited program service and marketing of receivers by April 30 next. Receivers have screens 10 by 7/4 inches, too small for convenient viewing, but pictures are bright and sharp and carry sufficient detail to depict emotions, when rather broadly played, in close-up or semi-close-up. Medium and long shots merely show the figures and are used mainly for entrances, exits, establishing settings, etc. In the main, story must be carried with two shots. Film takes of exteriors are sometimes intercut to good advantage. A member of Academy Research Council who witnessed some of the demonstrations found it difficult to concentrate on engineering features — his attention was constantly diverted to the action. This is as good a test of entertainment quality as any. Last June several N. Y. department stores demonstrated television reception, using the NBC transmissions. Pictures were mostly in the 5 by 4 inch range, JANUARY 1939 17