US2204250A - Television transmitting tube - Google Patents

Description

June 11, 1940. w c o 2,204,250

TELEVISION TRANSMITTING TUBE Filed May 31', 1938 WILL/7RD H. H/CKOK WZAL A TTORNE Y.

INVENTOR. W N

Patented June 11, 1940 UNITED 1 STATES TELEVISION TRANSMITTING TUBE Willard H. Hickok, Bloomfield, N. J., assignor, by mesne assignments, to R adio Corporation of America, New York, N. Y., a corporation of Delaware Application May 31,

2 Claims.

My invention relates to television transmitting systems and particularly to new and novel transmitting tubes and focusing arrangements for projecting thereon optical images and especially images of conventional motion picture film.

In present television transmitting arrangements, it is common practice to project an optical image of the object to be transmitted directly on a photosensitive electrode such as a mosaic electrode having a great number of individual mutually separated photosensitive particles which respond in photoelectric emission in accordance with the elemental areas of light and shade comprising the optical image. Such an arrangement of a transmitting tube and system has been used whether intelligence to be transmitted is derived from an illuminated object or by projecting light through a film on which the object is printed. The response of the mosaic electrode in photoelectric emission is not as great as that desired and in addition, the photosensitivity of the mosaic electrode is often impaired by the electron beam used in scanning the photosensitive particles to neutralize the electrostatic charges formed thereon under the influence of the optical image.

The principal object of my invention is to provide a new and improved television transmitting system utilizing a mosaic electrode type transmitting tube of high efliciency wherein the mosaic electrode operates over a more eflicient portion of its response characteristic. Another object is to provide a television transmitting system which is more sensitive to light and produces a higher signal output than those systems already in use. It is a still further object of my invention to provide a cathode ray transmitting tube having a higher signal output for a given light input.

In accordance with myinvention, I provide a system utilizing a mosaic electrode type trans- 40 mitting tube having a novelmosaic electrode capable of developing and storing an electrical replica of an optical image of an object focused on the electrode, which image is distorted or ex- 45 panded in a unilateral direction whereby a more effective electrical storage, a more sensitive systemfor given light input and amore responsive system for greater light input than is customarily used in conventional systems may be obtained.

These and other objects, features, and advantages of my invention will appear from the following description taken in connection with the accompanying drawing in which:

Figure 1 is a combination schematic and perspective view partially in section showing the 1938, Serial No. 210,965

principal details of my television transmitting tube and system; and,

Figure 2 is a perspective sectionalized view of a portion of the electrode structure incorporated in the tube shown in Figure 1.

In the illustrative embodiment of my invention shown in Figure 1, the television transmitting tube used with my new and improved system and incorporating a new and novel mosaic electrode will first be described. The tube comprises a highly evacuated glass envelope or bulb l of cylindrical shape with a tubular arm or neck section enclosing a conventional type electron gun. The bulb l encloses a flat target or mosaic electrode 2 symmetrically positioned in the envelope so that its front surface may be scanned by a beam of electrons from the electron gun and also may have projected upon it theoptical image to be transmitted. Since the image is produced by light from an object situated outside the tube, a portion of the tube such as the transparent window 3 is made optically uniform so that the image to be transmitted may be projected upon the mosaic electrode 2 with a. minimum of distortion by the lens 4, and preferably of spherical shape so that it may better withstand the atmospheric pressure from without the tube.

The electron gun assembly is of the conventional type and comprises a cathode 5 from which an electron stream may be drawn, a control electrode 6 connected to the usual biasing battery and a first anode l maintained positive with respect to'the cathode 5. The electron stream leaving the first anode I is accelerated, and concentrated into an electron scanning beam focused on the front surface of the mosaic electrode 2 by a second anode 8 which is preferably a conducting coating on the surface of the bulb I near and in the neck of the bulb but removed from that portion through which is projected the optical image to be transmitted. The first anode I and the second anode 8 are maintained at the desired positive potentials with respect to the cathode 5 by a battery 9. Conventional electromagnetic deflection coils ID are used to sweep the beam in one direction only across the target or mosaic electrode 2. In the modification shown the deflection coils are so arranged as to sweep the beam in a single plane which is perpendicular to the plane of the drawing. It is obvious that conventional electrostatic deflection plates may be substituted for the single set of deflection coils if desired.

In accordance with my invention, the mosaic electrode, as best shown in Figure 2, comprises a sheet of insulating material such as a sheet of mica H having on one side, or on the front surface, a discontinuous photosensitive structure of line formation and on the opposite side or rear surface of the sheet of mica a continuous coating of electrically conducting material. The discontinuous photosensitive structure comprises a great number of closely spaced but mutually insulated and electrically isolated photosensitized metallic conductors I2, each of which extends across the mica sheet H and is continuous from one edge of the mica sheet to the opposite edge. The mosaic electrode is positioned in the bulb l in such a manner that it may have an optical image projected on its front surface and so that it may be scanned by the electron beam which scans or sweeps across the metallic lines, preferably near the lower ends of the lines, such as along a path represented by the dashed line 53. 'In making the mosaic electrode 2, I select a sheet of mica ll of the desired area having a uniform thickness of approximately .002" thus obtaining a sheet of insulation sufiiciently thin and of sufficiently uniform insulating properes over its exposed surface without sacrificing mechanical strength or other desired properties. The front side of the sheet of mica H has deposited thereon a metal such as silver which may be highly photosensitized, which metal is deposited or otherwise applied to the sheet of mica as narrow continuous rectilinear strips or conductors M which extend from one edge of the sheet of mica to the other edge and are of low electrical resistance throughout their length. For low definition transmission of these conductorsare suffifcient, although for the presently proposed e41 line standard of television transmission a minimum of 441 strips or conductors t2 should be used. The conductors 52 are preferably of equal width and for low definition applications may be wider than the spaces between conductors, for example, I have made the width of the c'onductors'twice the width of the intervening spaces with 100 conductors occupying a width of 2 inches the length of the conductors being 1 inches long. For higher definition such as the 441 line proposed standard the spaces between conductors may be equal to the Width of the conductors and the size of the effective area of theelectrode may be larger such as 3 by 4- inches. The rectilinear conductors may be applied most conveniently by printing the sheet of mica with a line out having lines of the desired length and width, and inked with a silver containing printing vehicle, preferably finely divided silver powder, mixed to form a paste with a volatile binder, such as oil of Wintergreen or oil of rosemary. As an alternative method, the multiple line type of mosaic may be formed on the sheet of mica H by a process somewhat similar to that disclosed by Tedham et al., in their U. S. Patent 2,077,442, by vaporizing the metal to be deposited and condensing the metal on the sheet of mica through a grid-like mask composed of a screen of parallel Wires which cover the mica leaving parallel sections of the mica exposed so that the metal can condense thereon. During the evacuation process of the tube such volatile binders as may be present are removed and the metal lines or conductors l2 are oxidized and photosensitized'such as depositing thereon caesium or other alkali metal. A process for satisfactorily oxidizing such a mosaic electrode is disclosed by S. F. Essig in his U. S. Patent 2,065,570 and a process for sensitizing a mosaic electrode in his U. S. Patent 2,065,570.

The next step in preparing the mosaic electrode is to deposit on the rear side of the sheet of mica opposite the side which supports the individually separated -metallic conductors l2, the uniform coating of metal such as platinum or other conducting material M which serves as a signal plate for the mosaic electrode 2.

To strengthen the thin mica sheet II which carries the individual metallic conductors and the electrically conductive coating such as platinum on the opposite side and which is inherently weak because of its thinness, I prefer to use a relatively thick backing sheet l5 also preferably of mica and of the same shape and area as the sheet it. On the side of the backing sheet facing the coating of conducting material it, I provide a conductive coating it also preferably of metal such as platinum in good electrical contact with the platinum coating it to assure minimum electrical resistance between various points on the coating i l and the external circuit which is connected through the lead ll to a frame or clip member it! which grips the two edges of the mica and which'is in electrical contact with the coating it. Referring again to Figure 1, the frame or clip member is which is in electrical contact with the conducting material Hi or signal electrode is connected through the impedance 9 to ground and the second anode 8. In operation, the signal current flow in this circuit produces a voltage drop across the impedance l9 which may be impressed on the input electrode of a translating device 20 further amplified and applied to a transmitting network in a manner well known to the art.

Referring again toi igul'e 1, pictures of the object to be transmitted are printed on the photographic film 2! which, during the operation of the system, moves under constant velocity from the film reel 22 over the rollers 23 in the direction of the arrow 2d and is stored on the take-up reel 25. Intermediate the rollers 23, I provide a mask 26 which is provided with a narrow horizontal slot 27 which is substantially perpendicular to the direction of motion of the film 2!. To one side of the film 2i and in line with the slot 2'! of the mask 26, I provide a suitable light source such as an arc light 28 with a condensing lens 29 and a focusing l ns 30 between the light source and the slot 21, so that light from the light source is collected and focused upon the film it as a line of light in alignment with and along the horizontal slot 21. On the other side of the film 2i and between the lens system t and the mosaic electrode 2 and optically aligned therewith, I provide in accordance with my invention a lens system schematically illustrated by the cylindrical lenses 30' and 3! which spreads or uniformly distorts the light or image of the film in the slot 2'! in a direction perpendicular to the longer dimension of the slot, that is to say, in a direction parallel to the movement of the film as indicated by the arrow 24 or parallel to the longer dimension of the photosensitive conductors 82, The lens system 39 and 35 is so designed as to, be ineffective in spreading or distorting the light or image of the film in the slot in a direction parallel to the slot. It is, therefore, evident that the elemental line image of the film 2| controlled in width by the dimensions of the slot, is projected upon the mosaic electrode 2 as a true optical image in a direction parallel to the longer dimension of the slot but as an expanded image in a direction perpendicular to the longer dimension of the slot. The length of the slot is equal to or slightly less than the width of the intelligence printed on the film II and the width of the slot is determined by the resolution desired in the transmission of the intelligence. For conventional motion picture film, having a sound track, the length of the slot is preferably 20 mm. and for 100 line definition the width of the slot is approximately 0.007 inch.

In the operation of my new and improved system of television transmission using a transmitting tube having a novel mosaic electrode, the film is moved at a uniform velocity so as to se quentially project optical images of continuously varying intensity depending upon the composition of the subject matter printed on the film upon the mosaic electrode as a true optical image in one direction and as an expanded optical image in a direction perpendicular to the aforesaid direction. The electron scanning beam generated by the electron gun is focused upon the mosaic electrode 2 and scans the photosensitive and mutually separated metallic conductors I 2 preferably near one end of the mosaic electrode and near the ends of the conductors such as along the path I3 and is synchronized with the moving film in such a manner that the electron beam scans across the mosaic electrode once for each sequential elemental area of the film 2! which is exposed to the light through the slot and which is projected on the mosaic electrode 2.

It will be evident from the foregoing description of my invention that the photosensitive response of the mosaic electrode may be made greater with my system of television transmission than in previous systems Where the entire optical image to be transmitted is focused directly upon a mosaic electrode which is scanned by the electron beam in a series of lines from the top to the bottom of the electrode because in my system the mosaic electrode operates below its photosensitive saturation point or, in other words, over a lower portion of the light intensitysignal output characteristic curve since the light of one horizontal element of the image is spread over the entire photosensitive area of the mosaic electrode. For the same reason the charging period of the photosensitive line elements is more efliciently utilized inasmuch as the charging effect is limited to a period of time equivalent to one scanning line whereas in the conventional system above referred to, the charging period extends for a period of time equivalent to an entire frame period and only a small fraction of this frame period is utilized in the charging of the electrode. It will likewise be evident from the foregoing description that it is not necessary to scan the photosensitive elements over the surface on which the optical image to be transmitted is projected and that there is, therefore, no possibility of affecting the photosensitive response of the line like elements by the scanning electron beam.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or to the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed Without departing from the scope of my invention as set forth in the appended claims.

What I claim is:

1. A cathode ray television transmitting tube comprising an envelope a portion of which is light transmitting, an electrode assembly including an insulating base within said tube exposed to said portion, a light sensitive structure on one side of said base exposed to said portion, said structure comprising a plurality of equally spaced mutually insulated and electrically isolated elongated photo-electron emissive metal conductors of loW electrical resistance extending in a longitudinal direction substantially from one edge to the opposite edge of said one side of said base, an electrically conductive coating coextensive with and covering the opposite side of said base, means Wholly exposed to said light sensitive structure to generate an electron beam within said tube and means to scan said electron beam across substantially the entire width of said base, in one direction only and normal to the length of said conductors to scan substantially all of said conductors.

2. A television transmitting tube comprising an evacuated envelope a portion of which is transparent to light, an electrode structure including a sheet of mica within said tube exposed to said portion, a plurality of closely spaced continuous rectilinear photo-electron emissive silver conductors mutually insulated andelectrically isolated one from the other on one side of and extending substantially across the entire Width of said sheet of mica, a coating of metal coextensive with and covering the other side of said sheet of mica, an electron gun in said tube Wholly exposed to said conductors togenerate an electron beam, and means to scan said beam across said silver conductors in one direction only, in a direction normal to the length of said conductors and across substantially the entire sheet of mica.

WILLARD H. HICKOK.

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