US2048094A - Television receiver - Google Patents

Description

July 21, 1936. D. APPLEBAUM TELEVISION RECEIVER Filed June 21, 1932 -|NVENTOR fla /a BY 60% 0am ATTORNEY Patented July 21, 1936 UNITED STATES PATENT OFFICE 'mmifififim David Appiebaum, Los Angeles, Calif. Application June 21, 1932, Serial No. 818,484

3 Claims. (01- 250-35) This invention relates to television, and more particularly to a receiving system for television.

Such systems usually employ a source of light the intensity oi which varies with the received impulses, and which is caused to traverse or scan a screen, such as ground glass. The complete scanning to produce a complete image by variable illumination of the screen must be rapid enough to be within the period of the persistence of vision. Ordinarily, for this purpose, as many as ten to twenty complete images are produced in each second of time, for this purpose, corresponding to hundreds or thousands oi pulsations per second.

The scanning can be produced in any of a number 01. ways; as for example, a scanning disc rotated at a speed synchronous with the light variations, in which disc there are a number of apertures arranged in a spiral. As the light shines through one aperture, the movement of the disc causes this light to traverse the screen,

the line so'produced having linear variations in light intensity. After this e" is produced, the next aperture is immediately active'to trace an adjacent line, and this is repeated so that for one complete revolution of the disc, there are produced as many lines of varying illumination as there are apertures in the disc. The height of the image is the radial distance from the outer- .most aperture on the spiral to the innermost aperture. Succeeding rotations produce succeeding complete linear scannings.

Since such scanning schemes or their equivalents are well-known, further description thereof is unnecessary.

In the use oi ordinary light, it has been common to use a neon globe, which apparently had the advantage of being very quickly variable as regards light emission to comply with the received impulses. However, the degree of illumination has never been entirely satisfactory; inasmuch as a very high degree or intensity is needed to utilize the effect of the persistence of vision. This necessitated the use of a quite small screen to produce a sufliciently brilliant image. Furthermore, the response to these impulses is not exactly instantaneous; and finally, even it the image-is produced as often as ten or more times per second, objectionable and flicker are still noticeable.

It is one of the objects of this invention to provide a television receiver that obviates these disadvantages. In this way it is possible tame a much larger screen, if desired, that can be simul taneously viewed by a large number or people.

It is another object of my invention to make I it possible to illuminate each spot of the screen in such a way that its illumination is not only intense, but is caused to persist, so as to produce a fiickerless image.

These results are accomplished by using, in place of a light source, a source of radiations of extremely short wave length, such as X-rays. These radiations in turn are converted into light rays, as by a fluorescent screen. This screen re- '10 mains illuminated for a period sufiicient to bridge the period 0! the persistence of vision. It is also intensely iiluminable by producing a high intensity of radiations. The intensity of these radiations, furthermore, is instantaneously controllable in accordance with the received impulses, and accordingly more faithful reception is produced.

It is another object of this invention to make it possible to control a source of high frequency invisible radiations in accordance with the rapidly varying received impulses. I

It is another object of this invention to obviate the necessity of using a very intense light source, and yet obtain an intensely illuminated screen, capable of afl'ecting the eye to such an extent as to utilize to a high degree the eiiect oi the persistence of vision.

Referring to the drawing:

The single figure is a diagram of one form of the invention.

In this figure, the screen I upon which images are visible is arranged in the path oi high frequency radiations, such as a beam defined by the dotted lines 2 and 3. In this case the beam 2-3 is produced by short wave radiations,- of the order of X-ray radiations, of intense penetrating power, in a manner to be hereinafter described. The screen I. is madeup of a backing or support 4, such as cardboard or thin metal that is pervious-to the rays, and a layer 5 of fluorescent material. This layer 5 is arranged to be visible. The fluorescence or phosphorescence can be obtained by well-known means such as solutions 01' barium platinocyanideor calcium tungstate, applied as a paint to the screen.

The X-ray emanations preferably are arranged to radiate from a point source 8 on an X-ray target or anode i. By providing a point source, the radiations can be passed directly to the screen without the need of any optical lens systems. The beam 2-8 is a cone. Interpos'ed between this source and screen I, is a scanning device, such as a scanning disc 8 rotated by a motor 9. This motor is operated in synchronism with the received television impulses so that the disc I can produce a scanning eifect in proper relation to these impulses. Since beam 2-3 is a cone, the disc I .traversing the beam controls the scanning of elemental areas of screen I in substantial exact accordance with the area of the beam where disc I intercepts it, without the need of lenses.

The disc 8 can be provided with a series of apertures, one of which is shown at l0, arranged in a spiral around the axis of the disc. The angular spacing of these apertures corresponds to the height of the image perpendicular to the plane of the drawing. In this way each aperture ill sweeps across the field oi screen I and produces a line" transverse to the screen; in this instance, in aplane perpendicular to the drawing. Thus a "line" is in this way being scanned by the thin pencil of rays 22. The disc 8 can be rotated at the usual rate, that is from about ten to twenty times per second. Each rotation corresponds to a complete image, scanning. Disc 8 is made from sufiiciently thick metal to be impervious to the X-rays except at the apertures Hi. It is, of course, also understood that the beam 2-4 is invisible but serves to excite the fluores cent layer 5 to intense luminosity wherever the beam strikes it through one of the apertures Ill. The phosphorescence produced by the striking of the X-rays on the layer 5 persists for an appreciable period, and accordingly the images produced in succession on screen I are made up of lines of light that do not immediately disappear when the X-ray beam leaves this line. of course,

appropriate impervious shields are provided to confine the activity of source 8 to the region required. I

By making the source 6 sufllciently intense, screen I can be moved quite far away from the source 6, to produce a large image that can be viewed by a large number of people simultaneously. This is especially useful in theatres or auditoriums. The area of the image thus formed increases as the square of the distance of the screen from source 6.

The intensity of the X-ray emanations can be varied in a number of ways to comply with the received impulses. A hotfilamentary cathode I! can be used, and electrons therefrom can reach the target 1, as in the conventional Coolidge tube. The hardness can be varied as by the aid of a control electrode l9 interposed in the electron path, the potential of which electrode with respect to the filament I! can be varied directly in accordance with the received impulses. In this case, however, I have shown a so-called Liliienfeld type of X-ray tube, utilizing several additional electrodesyall of which are supported in an envelope II. The X-rays are produced, as is well understood, by directing a stream of electrons travelling at a high rate on the sloping face of the target I. This stream emanates from the cathode I2, heated as by current produced by-a battery I 3. A resistance I4 is bridgedzacross the filament to act as a potentiometer. An auxiliary anode i5 is spaced from the filament i2 and is connected externally of the tube through a. source of direct current potential l6. This'source can be of the order of 1500 volts and serves to draw the electrons from the cathode i2 toward the target I. The electrons are further accelerated by the aid of a supplemental tubular electrode ll through which the electrons pass. The anode I is connected to electrode i1 through':a high potential direct curent source such as I 8. The potential of source It can be as high as 15,000 volts or more. In this way an intensely rapid moving stream of electrons is caused to strike the taret I. v g The volume of electrons reaching target I is controlled by the control electrode l9, which can be in the form of a grid. By varying the relative potentials of the filament l2 and grid l9, as in ordinary three-electrode electronic emission devices, the intensity of electron flow can be made to vary instantaneously with the pulsations of electromotive force impressed across electrodes i2 and I8. Accordingly, these two electrodes l2 and ll are connected to opposite sides of a source III of received impulses. By varying the tap on potentiometer I the grid I! can have a bias with respect to cathode it, such that when no impulses are received, the electron stream is Just sufiicient to produce a slight glow on screen I. However, when the impulses are received the electrons are permitted to pass the control electrode I 9 through the tubular electrode I! and on to a point 8 on target 1-, to produce intense luminosity.

If desired, a supplemental biasing means, such as battery 2| can be provided in the control elec- 25 trode lead.

Electrodes l2, l9, and II virtually form a three electrode device for providing a reservoir of electrons for the cathode-anode arrangement "-1. The control is intensely rapid and can faithfully follow the reception of extremely high frequency impulses by source 20. Only a low degree of amplification need be provided for by electrodes i2, i9 and I5. Furthermore, the hardness of the tube, being dependent upon the potential difference of source I 8 is uniform.

-By the aid of this control, the intensity of the X-ray beam 2-3 is made instantaneously responsive to the received impulses. When using the Coolidge type of tube, the hardness is varied. In either case, the intensity or hardness or both serve to determine the intensity of luminescence of screen I The glow of phosphorescence on layer 5 persists even after the X-rays leave any particular spot thereon, and therefore help to provide a continuous image, rather than an interrupted image as in the usual television receiver. It is with this in mind that I have used the term persistence in myclaims. That is, the visible light persists after the X-rays have ceased to act on the screen.

I claim:

1. In a device of the character described, an evacuated vessel, an electron emitting cathode therein, an anode cooperating with said cathode for drawing electrons from the cathode, means forming a spaced pair of electrodes so arranged that the emitted electrons traverse the space between said spaced pair of electrodes to impinge upon one 01. them to cause an X-ray emission therefrom, means for impressing a potential difference between said spaced pair of electrodes so that the electrode upon which the electrons impinge forms an anti-cathode, a control electrode I inside said vessel for varying the electron stream,

and means for passing signaling impulses to the control electrode.

2. In a device of the character described, an-

therefrom, means for impressing a uniform potential difference between said spaced pair of electrodes so that the electrode upon which the electrons impinge forms an anticathode. a control electrode inside said vessel and adjacent the cathode for varying the electron stream, and means for impressing signaling impulses between the cathode and the control electrode.

3. In a device of the'character described, an evacuated vessel, amlectron emitting cathode therein, ansanode cooperating with said cathode for drawing electrons from the cathode, means forming a spaced pair of electrodes so arranged that the emitted electrons traverse the space hetween said spaced pair of electrodes to impinge upon one of them to cause an X-ray emission therefrom, means for impressing a uniform potential difference between said spaced pair 01' electrodes so that the electrode upon which the electrons impinge forms an antlcathode, a control electrode inside said vessel for varying the electron stream, and means for impressing signaling impulses between the cathode and the control electrode, one of the spaced pair 01' electrodes being near the anode and adapted to influence the electrons passing the anode. v

DAVID APPLEBAUM.

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