US2297499A - Television transmitter - Google Patents

Television transmitter Download PDF

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Publication number
US2297499A
US2297499A US353685A US35368540A US2297499A US 2297499 A US2297499 A US 2297499A US 353685 A US353685 A US 353685A US 35368540 A US35368540 A US 35368540A US 2297499 A US2297499 A US 2297499A
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United States
Prior art keywords
current
tube
grid
curve
voltage
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Expired - Lifetime
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US353685A
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English (en)
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Rappold Armin
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Individual
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Individual
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/222—Studio circuitry; Studio devices; Studio equipment
    • H04N5/257—Picture signal generators using flying-spot scanners
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
    • H01J29/18—Luminescent screens
    • H01J29/182—Luminescent screens acting upon the lighting-up of the luminescent material other than by the composition of the luminescent material, e.g. by infra red or UV radiation, heating or electric fields

Definitions

  • the well known after-luminosity of the fluorescent material causes errors in the modulation mixture, which errors are small enough and hence negligible only if the duration of such after-efiect be much shorter than the duration of scanning a picture point.
  • tubes V1, V3, V4 may
  • tube V may be any well-known type of grid-controlled amplifier tubes
  • tube V may be any well-known form of multi-grid mixer tube.
  • the cathode is represented by a dot and the successive electrodes arranged vertically thereabove are respectively; the first control grid, the anode-grid; the second control grid, the shield grid, and the. output plate or anode.
  • the control grid of tube V3 is conductively connected to the output electrode of the photoelectric cellelectron-multiplier P and the amplified D.
  • C. output of tube V: is supplied over a separate lead to a suitable transmitting modulator (not shown).
  • the cathode is designated by a dot while the remaining electrodes are represented in the conventional form.
  • the differential or residual output of tube V2 (which in accordance with the invention has been compensated to remove errors which tend to be introducedby reason of the after glow-of the fluorescent screen to which cell P is exposed), is applied to another conventional amplifier tube (not designated) which also feeds the same modulator through a condenser as shown.
  • the voltage which is produced by the photoelectric cell (which voltage is not only a iunction of the actual light value of an image point being scanned but also of the after-glow or lag of the fluorescent screen material to which the cell is exposed) is used to control two separate grid-controlled amplifier tubes in parallel.
  • One of these two tubes may be considered a main amplifier tube, and the other may be considered an auxiliary or compensating tube.
  • the outputs of the two tubes are fed in phase opposition to two separate control grids of the multigrid mixer tube.
  • the said auxiliary tube is con nected so that it operates at a variable point or. its gridwoltage vs. plate current characteristic curve which point at any given time is a function of the output voltage of the main amplifier.
  • the voltages from the main and auxiliary tubes are impressed respectively on the first and second control grids of the mixer tube.
  • the working point of the auxiliary tube is determined by an impedance connected in the cathode lead thereof the impedance being proportioned.
  • the output of the auxiliary tube produces at the secondcontrol grid of the mixer tube a voltage which is sufiicient to neutralize the potential applied to the first control grid of the mixer tube from the main amplifier corresponding to the D. C. component of the cell current.
  • the two voltages applied to said control grids of the mixer tube do not follow identical laws so that there is a residual or differential voltage in the output circult of the main tube.
  • this residual voltage can be made to correspond to the actual light value of the image point under consideration and is substantially free from the after-glow" effect of the fluorescent material.
  • P denotes a photo-electric cell located in the input circuit of a secondary emission multiplier.
  • the cell P is arranged in the usual manner to be, energized by light from the fluorescent screen being scanned by the cathode ray.
  • A. scansion of an individual image point Suppose a diaphragm having an aperture of the size of an image point is scanned by means of a cathode ray tube serving as source of light. Suppose also that the spot of the cathode beam projected on the film or on the diaphragm be smaller than an image point, and the speed of scanning be so high that the scansion of an image point takes 2-1(I
  • the curve a illustrates the penetrability of the diaphragm, the penetrability being represented here as f (t) that is, a function of the time t.
  • Curve 1 shows, likewise as a function of time 1 (t), the quantity of light passing through the aperture of the diaphragm.
  • the scansion pattern element on the screen that is, the pattern element allotted to the scanned aperture of the diaphragm, continues to glow even when the beam has passed on and is acting on other elements of the scansion pattern, the luminosity of which, however, in this case does not impinge upon the diaphragm and does not produce a photo eifect.
  • Curve b thus illustrates how the brightness of the pattern element determined by the diaphragm decreases.
  • This curve is a. function of e, as will be seen from the'formula where 1-e is the time taken by the luminosity diminishing to 1/e of the maximum value.
  • the voltage represented by curve 0, Fig. 2 is conveyed to the grid In Fig. 2d part of the grid-voltage vs. plate current characteristic curve of V4 is shown apart.
  • a certain value of the resistance Ra may be determined by means of the value L known from the curve e, namely, a resistance Ra that acts to cause during the interval of time 4-l0-"2-10-" sec., that is, during 2-10- sec. a drop of potential equal to the voltage of Up in 4-10- sec.
  • Ra and R1 By suitably dimensioning Ra and R1; these integrals may be made to equal one another in case a number of picture points of the same brightness are scanned. Equally, where image points of different intensities of brightness are concerned the integrals may be made to be proportional to the respective intensities.
  • a television transmitter in which pictures projected on a fluorescent screen having afterglow effects are scanned by an electron beam and the light from the scanned spot in the screen is projected onto a light sensitive cell, the combination of means for deriving from said cell two currents which are variable in accordance with the light values of the points scanned on said screen, one of which currents difiering in magnitude from the other by an amount proportional to the actual light value of the picture area corresponding to the spot being scanned, and means for combining said two currents to produce a resulting variable current corresponding substantially to variations in actual light values or the picture areas being scanned and substantially free from the errors which tend to be introduced by the after-glow" of said screen.
  • a television transmitter according to claim 1 wherein the means for combining the two currents comprises a multi-grid tube having one grid controlled by one current and another grid controlled by the second current.
  • a television transmitter in which pictures projected on a fluorescent screen having afterglow efiects are scanned by an electron beam and the light from the scanned spot on the screen is projected onto a light sensitive cell having an energizing circuit in which a current pulse is produced on the scanning of each elementary area of said screen, each current pulse having an initial value corresponding to the actual light value of the elementary picture area being scanned and decreasing in value during the afterglow period, means deriving from said cell circuit current pulses in substantially undistorted form, means for deriving from said cell circuit a second series of current pulses having an initial value differing from said first series of pulses by an amount proportional to the actual light values or the corresponding picture areas, and means for combining said two series of current pulses to produce a resultant series of current pulses corresponding in value substantially to the actual light values of the picture areas being scanned and substantially free from the errors which tend to be introduced by the after-glow" of said screen.
  • each current pulse having an initial value corresponding to the actual light value of the elementary-picture area being scanned and decreasing in value during the after-glow period
  • means deriving from said cell circuit two series of current pulses having substantially the same rate of decay during the after-glow period but having different rates of increase in the initial portions of said pulses, and means for combining said two series of current pulses to produce a resultant series of current pulses corresponding in value substantially to the actual light values of the picture areas being scanned and substantially free from the errors which tend to be introduced by the afterglow of said screen.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
US353685A 1939-09-05 1940-08-22 Television transmitter Expired - Lifetime US2297499A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE228104X 1939-09-05

Publications (1)

Publication Number Publication Date
US2297499A true US2297499A (en) 1942-09-29

Family

ID=5867020

Family Applications (1)

Application Number Title Priority Date Filing Date
US353685A Expired - Lifetime US2297499A (en) 1939-09-05 1940-08-22 Television transmitter

Country Status (4)

Country Link
US (1) US2297499A (enrdf_load_stackoverflow)
BE (1) BE439852A (enrdf_load_stackoverflow)
CH (1) CH228104A (enrdf_load_stackoverflow)
FR (1) FR868878A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2495534A (en) * 1945-10-26 1950-01-24 John W Meaker Apparatus for perforating sheet material
US2617879A (en) * 1948-06-18 1952-11-11 Rca Corp Signal quantizer
US2764697A (en) * 1950-11-02 1956-09-25 Rca Corp Image scanning system

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE871908C (de) * 1942-03-27 1953-03-26 Telefunken Gmbh Schaltungsanordnung fuer Fernsehbildzerleger

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2495534A (en) * 1945-10-26 1950-01-24 John W Meaker Apparatus for perforating sheet material
US2617879A (en) * 1948-06-18 1952-11-11 Rca Corp Signal quantizer
US2764697A (en) * 1950-11-02 1956-09-25 Rca Corp Image scanning system

Also Published As

Publication number Publication date
CH228104A (de) 1943-07-31
FR868878A (fr) 1942-01-19
BE439852A (enrdf_load_stackoverflow)

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