US2163545A - Apparatus and method for television transmission - Google Patents

Description

June 20, 1939.- 2,163,545

APPARATUS AND memos FOR TELEVISION TRANSMISSION s CLOTHIER' ET AL Filed Aug. 51, 1937 Patented .iso, 1939 'rus Amr- METHOD son TELE- vrsron TRANSMISSION Stewart nominee, llrvin'gtor and name o.

Hogencamp, ,Maplewood, N. 3., asslgnors to Kolorama laboratories corporation of New ilersey Inc Newark, N. 3., 2.

Application August 31, 1937, Serial No. 161,730.

7 Claims (oi. its-v.3)

Our invention relates to improvements in anp atus and methods for television transmission.

' While the various-apparatus and methods proposed heretofore for television transmission have been effective to transmit a recognizable picture atleast ovenairelatively short distance, each of the same has been found to involve necessarily intrinsic structural ch 'racteristics and principles giving rise to problems ofmanufacture and, generally, definite limitations in the way of detail of the image reproduced at the receiving station, and output level of the picture signals produced by the transmitting apparatus for a given intensity the view or subject being tele-,

size, the uniformity of photosensitivity of the 30 particles over the entire mosaic surface or area, and the prevention of leakage between adjacent particles. These. requirements in the television transmitting apparatus of this general type give the same the definite limitations referred to.

In television transmission apparatus of the general type disclosed in Patent No. 1,773,980 issued to Philo T. Farnsworth, there isno requirement for a mosaic, photosensitive screen, but there is, however, 0 fiection in horizontal and vertical directions, of

electrons issuing simultaneously. from the individual eementatl areas of a photosensitive screen, with respect to a single, remote and relatively minute anode disposed on the far side of a small 45 aperture in a metallic plate. Suchapparatus has been found' to involve problems due to 00: curring distortion of the electron stream, and the fact that each ofthe individual rays of electrons making up the entire stream isnot focused per-. 50 fectlyon theanode as the stream is deflected forscanning.

with the foregoing inmind, an object, of our invention is the provision of an improved apparatus and method for television transmission which 55 avoids the difl lculties referred to,

and: by which a detail or picture definition the requirement for simultaneous .de-

' mica or glass.

substantially greater output level of picture signal can be obtained, for a given intensity of illumina-v tion of the view or subject being televised and for. a given amount of signal amplification at'thetransmitter, than has been possible with the various apparatus and methods proposed heretofore for the same purpose.

Other objects and advantages will hereinafter appear.

Our invention resides in the improved construction and method of .operation hereinafter described and claimed.

Forthe purpose of illustrating our invention, an

embodiment thereof is shown in the drawing,

wherein:

Figure l is a simplified, diagrammatic view of television transmission apparatus constructed and operating in accordance with our invention;

Figure 2 is an enlarged, fragmentary, sectional view, the section being taken on the line 2-2 in Fig.1; and

Figure -3 is a view similar to Fig. 1, modification.

In the drawing, the reference numeral ill designates an evacuated tube provided at an end 'thereof with a photosensitive screen ii. The

screen I i may be formed onthe inside surface of the transparent end wall of the tube; and be in the form of a continuous, semi-transparent coating of silver over which is silver oxide and'cesium, as will be-well understood by those skilled in the art. As an alternative, the screen it may be in the formof a wire screen of fine mesh, photosensitized and supported within the tube in spaced relation with respect to the adjacent end wall thereof. I

At its opposite end, the tube i0 is providediwith means, in the form of a gun l2'of a suitable conventional construction, for developing a ray it of electrons, directed at and focused on a screen M; The screen it is supported between the photosenshowing. a

sitive screen H and the gun l2, and the edge thereof is at east slightly spaced from thewall of the tube.

The screen I4 is. imperforate, that is, there are no apertures or openings in the eifectlv'e or operating area of the same, and at least this area is' made entirely also be the axisof the tube, is a single anode l5 of elemental 'size compared to the areas of the of insulating materiahsuch as line through the respective screens. Asshownin Fig. 2, the anode i5 may be in the form of a small'wire loop formed from the end of a supporting and'connecting wire I6 which may be encased in a glass stem I'I extending radially inwardly from the wall of the tube.

An electrode -I8, which may be in the form of a metal ring. is supported adjacent to and on the gun side of the screen I4. A similar electrode I9 A saw-tooth voltage wave at line frequency is supplied by a generator 20 and impressed across deflecting plates ii. A saw-tooth voltage wave.

at the frame frequency is supplied by a generator 22 an'd impressed across deflecting plates 23. In this way, the ray I3 of electrons is deflected simultaneously in horizontal and vertical directions to cause it to scan the adjacent surface of the screen I I in a conventional manner.

Synchronizing and framing signals are also supplied by the generators 2.0 and 22, respectively; and after amplification by a common. amplifier 24 are fed to a modulator 25 and thence to the transmitter 26.

A light image of the view or subject 21 for transmission isiocused by a suitable lens system 28 on the adjacent surface of the semitransparent, photosensitive screen II.

In operation, the anode I5 and the electrodes I8 and I9 are maintained at potentials positive with respect to the potential of the screen II, and the potentials of the anode I5 and the electrode I8 are positive with respect to the poten tial of the electrode I9, as represented in the Y drawing. It will 'be'understood that for anyparticular condition of operation, adjustments will be made to place the respective potentials of the anode I5 and the electrodes I8 and I9 at the values for most efficient operation. As an example, the potential of the anode I5 with respect to that of the screen II might be of the order of 1,000 volts positive.

In explaining the manner in which our im proved apparatus is believed to operate, the electrical action at only one of the minute, elemental areas or points 29 of the entire eflective portion of the photosensitive screen II, will first be considered. Electrons are emitted from the point 29 in amount corresponding to the intensity, at the instant, of the light ray 30 coming from the corresponding point of the subject 21, and the amount of electronic emissionvaries lnstantaneously with and directly proportionally tooccur ring variations in intensity of the light, ray 30. At any instant, the electronic emission directly at the photosensitive point 29'takes place in many different directions and in a more or less hap-'-' hazard fashion. However, the strong attraction of the anode I5 for the electrons causes them to fall in line and'travel a' common, straight path 3|, at high velocity, to the anode I5. Some of the electrons will be absorbed by or passed to ground by way of the anode I5, but the remainder, still at a relatively high velocity, will pass on through thepinhole aperture 32 in'the anode and continue along the straight path 3| to the complementary or corresponding elemental area or point 33 of the adjacent surface of the screen I4,

, whereupon an electrostatic charge is developed or induced on theopposite side ofthe screen 14, directly opposite the point 33. Such electrostatic charge, like the-original electronic emission from the point 29 of the photosensitive screen I I, corresponds in value to the intensity, at the instant,

, electrode I8.

"operating action. By variation to a maximum. Similar electrodes of the light ray 30, andvaries instantaneouslywith and directly proportionally to occurring variations in intensity of the light ray 30.

When the electron ray I3, the intensity of which is constant, strikes the screen I4 at the point 33 during the scanning action, the electrostatic charge referred to is instantaneously neutralized bythe electrons of the ray, but only such number of electrons are taken or absorbed from the ray as is required to neutralize the charge. The remainder of the electrons of the ray I3 are collected by theelectrode I8 and cons'titute the picture current or picture signal for that particular point of the subject 21 being analized at the instant.

The. picture signals are'taken from the collector electrode I8 by aconnection 34 and supplied to a picture-signal amplifier 35, from whence they pass to the modulator 25 and the transmitter 26.

The electrical action at each of the other minute, elemental areas or points of the entire effective portion of the photosensitive screen II is 1, are designated by the same respective'reference numeralsas the latter. In this case, however, the electron gun I2 and the collector electrodeI8 are on the same side of the screen I4 as the photosensitive screen' II, and neutralization of the electrostatic charges by the electrons of the. scanning ray I3 takes place on this side of the screen I4. Also, the screen I I is backed by a supporting metallic plate 36 from which the picture signals may be taken instead of from the d The arrangement and operating action, otherwise, is similar to that in Fig.

In Fig. 3, oppositely directed, conical electrodes 31 and 38 are shown on opposite sides of the anode I5, and both are maintained at potentials positive with respect to that of the screen I4.

The potential of either or both oi the electrodes 31 and 38 may b negative with respect to that of the anode I5. While use of theelectrodes 31 and 38 is not essential, it is seen thatthe electricalinfluence of the same might improve the of the respective potentials on the electrodes ,3! and 38, the size of the electrostatic image on the adjacent surface of the screen I4 may be controlled, and, also, the

numberof effective electrons reachingthis surface by way of the aperture 32 may be met be embodied in the construction shown inFig. 1.

aspect thereof, it will be seen that this resides in a new method of operation in which electrons, emitted from the individual, elemental areas or points of the entire effective portion of a photosensitivescreen, are caused to converge-simultaneously toward a'common focal regio r fjremote from such screen, this region in the embodiment disclosed being that immediately at or about the anode I5. Also, in our new method of operation,

Considering our invention from thebroader electrons are caused to travel toward the respective, individual elemental areas or points of the entire effective portion of a screen, such as the screen It, and simultaneously in paths diverging irom a common focal region remote from this screen.

Furthermore, in our new method of operation, it will be seen that electrons are caused to travel from any one, individual, elemental area or point of a first screen, such as the point 29, toward a corresponding elementalarea or point of a second screen, such as the point 33, and along paths which substantially intersect the respective paths of simultaneous and similar travel of electrons from the other individual, elemental areas or points of the first screen.-

Another important aspect of our invention resides in the operating step wherein electrical conditions occurring at the individual, elemental areas or points of the entire portion of a screen, such as the photosensitive screen II, are simultae neously utilized to produce, at the respective and corresponding individual, elemental areas or points of the entire portion of a second screen,

such as the screen [4, electrical conditions corresponding respectivelyin value to said firstmentioned electrical conditions.

As to the construction of our improved appa-' ratus, it will be seen that this does not embody the undesirable mosaic screen to be found in some of the various constructions of television transmitting tubes proposed heretofore, and, furthermore, avoids the various difliculties of manufacture and operation referred to before.

It will be understood that various modifications, such as in the size, shape and arrangement of" the parts, are possible without departing from the spirit of our invention or the scope of the claims.

We claim as our invention: I

1. In apparatus for television transmission, a

photosensitive screen, a second screen, means for causing the travel of electrons from each individual elemental area of said first screen toward a corresponding elemental area of said second screen andalong a path which substantially intersects the respective paths of simultaneous andsimilar travel of electrons from all other individual elemental areas of said'flrst screen at a common focal point intermediate said screens, aind means including a cathode ray gun structure for scanning said second screen with an electron beam to develop picture signals.

2. In apparatus for television transmission, a photosensitive screen, a second screen, a single ring anode of minimum surface area with an aperture of elemental sizecompared' to the respective areas of said screen, said anode bein disposed intermediate said screen and substantially on a line through the respective centers of said screens, and means including a cathode ray gun structure for scanning said second screen to develop picture signals.

3. In apparatus for television'transmission, a photosensitive screen, a second screen of insulating material, a single apertured ring anode of elemental size compared to the respective areas of said screens, said anode being disposed intermediate said screens and operating to effect travel of electrons from the individual elemental areas of said photosensitive screen to the respective and-corresponding elemental areas of said second screen and simultaneously along paths which intersect in the region of said anode, means including a cathode-ray gun structure for developing a ray of electrons and directing the same at said second screen, and means for deflecting said ray to cause the same to scan said second screen.

4. In apparatus for television transmission, a photosensitive screen, a second and imperforate screen ,at least the eflective portion of which is entirely of insulating material, a single centrally apertured anode of elemental size compared to the respective areas of said screens, said anode being disposed intermediate said screens and sub-' stantially on a line through the respective centers of said screens, means including a cathode-ray gun structure for developing a ray of electrons and directing the same at said second screen,

means for deflecting said ray to cause the same to scan said second screen, and an electrode disposed between said second screen and said ray-deflecting means.

5. In apparatus for television transmission, a tube provided at one end thereof with a photosensitive screen substantially perpendicular to the I corresponding elemental areas of said secondnamed screen and along paths which intersect said axis at a common focal point, and means for deflecting said ray of electrons to cause the same to scan said second-named screen.

6. In apparatus for television transmission, a tube provided at one end thereof with a photosensitive screen substantially perpendicular to the longitudinal axis of'the tube, a lens system for projecting onto said screen a light image of the subject for transmission, an electron gun at the other end of said tube for developing a ray of electrons, a screen disposed in said tube between and spaced from the photosensitive screen and said gun and being substantially perpendicular to said axis, said second-named screen consisting entirely of imperforate insulating material at least in the operating area thereof, means disposed between said screens and operating to effect travel of electrons from the individual elemental areas of said photosensitive screen to the respective and corresponding elemental areas of said second-named screen and simultaneously along paths each of which intersects said axis at a common focal point, and means for deflecting said ray of electrons to cause the same to scan said second-named screen.

7. In a television transmitter tube including a photosensitive screen at one end,

- a second.screen of imperforate insulating material spaeed from said first screen, means intermediatejsaid screens for causing electrons emitted from said photosensitive screen to travel to said second screen, 'and means including a. cathode-ray gun structure for scanning said second a cathode-ray I screen with an electron beam to develop picture signals.

STEWART L. CLO'I'HIER. HAROLD C. HOGENCAMP.

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