US2193857A - Television receiving system - Google Patents

Television receiving system Download PDF

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Publication number
US2193857A
US2193857A US168122A US16812237A US2193857A US 2193857 A US2193857 A US 2193857A US 168122 A US168122 A US 168122A US 16812237 A US16812237 A US 16812237A US 2193857 A US2193857 A US 2193857A
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United States
Prior art keywords
screen
picture
scanning
light emitted
time
Prior art date
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Expired - Lifetime
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US168122A
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English (en)
Inventor
Bouwers Albert
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RCA Corp
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RCA Corp
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Publication date
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Publication of US2193857A publication Critical patent/US2193857A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/66—Transforming electric information into light information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/66—Transforming electric information into light information
    • H04N5/68—Circuit details for cathode-ray display tubes

Definitions

  • a second method of transmitting pictures consists in scanning the picture to be transmitted at a speed which is determined by the brilliancy of the picture elements of the picture to be transmitted which are successively scanned whereupon in dependence on said speed a carrier wave is modulated and emitted.
  • the oscillations obtained after detection are supplied to the device for deflecting a cathode ray beam in a direction parallel to the scanning sponding picture elements of the picture to be lines with the result that the cathode ray beam is moved at the receiver at. a variable speed over a screen arranged within the tube, said speed being dependent on the brilliancy of the corretransmitted.
  • the invention is more particularly concerned with a television receiving arrangement in which the cathode-ray tube comprises a screen which becomes luminous by electron bombardment and has the property that a non-linear relation exists between the time during which the electrons strike the screen and the quantity of light emitted.
  • Cathode ray tubes which have a screen that emits light upon electron bombardment and wherein anon-linear relation exists between the time of exposure and the quantity of light emitted have previously been suggested in themselves for television purposes.
  • a tube wherein the screen has the characteristic curve desired is a tube which has a screen consisting of refractorymaterial which is raised to incandescence by electron bombardment. Tubes having similar characteristics but with different screens may, of course, be used.
  • the system according to the invention consists, therefore, in a television receiving system of the kind wherein the received oscillations obtained after detection are supplied to the above-mentioned device for deflecting the cathode ray beam in a direction parallel to the scanning lines and wherein the cathode ray tube comprises a screen which becomes luminous when struck by electrons and which has the property that there exists a non-linear relation between the time during which the electrons strike the screen and the quantity of light emitted.
  • the invention has for its purpose, therefore, to procure an improvement of the television receiving arrangement above referred to, this improvement consisting in that a carrier wave, modulatedby the received picture currents, is supplied to the deflecting means of the device for deflecting the beam of cathode rays in a direction parallel with the scanning lines.
  • Figures 1 and 2 each shows one form of construction of the circuit arrangement according to the invention.
  • Figure 3 shows, for example, a response curve for a cathode ray tube screen.
  • the television receiving arrangement represented in Figure 1 comprises a cathode ray tube 2 equipped with an electrode system for generating a beam of cathode rays and consisting at least of a cathode 4 and an anode 5.
  • a cathode ray tube 2 equipped with an electrode system for generating a beam of cathode rays and consisting at least of a cathode 4 and an anode 5.
  • To deflecting plates 8 is supplied an alternating voltage which is produced by a device Iii for the deflection of the beam of cathode rays in a direction parallel with the scanning lines, hereinafter called horizontal scanning device, said voltage having a saw tooth curve.
  • two deflecting plates i2 are provided to which is fed a saw tooth potential produced by a device M for deflecting the beam of cathode rays in a direction normal to the scanning lines, this device being hereinafter called vertical scanning device.
  • the receiving arrangement furthermore comprises an amplifier it to which are supplied the received modulated oscillations and which may be designed for frequency transformationof the received carrier waves.
  • the oscillations occurring in the output circuit of the amplifier [6 are supplied to a detector IS, in the output circuit of which low frequency picture currents and synchronizing impulses occur, which impulses are transmitted for the purpose of synchronizingthe saw tooth voltages produced by the devices l and M.
  • a filter 28 serves to separate the synchronizing impulses and the picture currents, Whereas a filter 22 is provided for splitting up the synchronizing pulses into line pulses and picture pulses.
  • the line impulses which are emitted by the transmitter at the end of each scanning line, are supplied to the horizontal scanning device l0, Whereas the picture'impulses-which occur at the end of the'scanning of each picture, are applied to the vertical scanning device [4.
  • the low frequency picture currents set up in the output-circuit of the detector l8, if desired after having been separated from the synchronizing impulses, are modulated on a carrier wave generated by a local oscillator 24 and the modulated oscillations thus produced are supplied to the deflecting plates 8.
  • the means for modulating the picture currents on the oscillations generated by the local oscillator 24', is designated by 26 in the'drawing.
  • Figure 2 shows a form of construction in which the modulated oscillations occurring in the output circuit of the amplifier l6 are supplied torthe deflecting plates of a cathode ray tube without interposition of a detector. Otherwise the circuit arrangement exactly corresponds to that represented in Figure l.
  • the cathode ray tube 2 comprises a screen which has the property that a non-linear relation existsv between the time during which the electrons-strike the screen and thequantity of light emitted as a function of the time during which the electrons strike the screen may consequently have a shape as illustrated in Figure 3, where L is the quantity of light emitted and T the time during which the electrons strike the screen, hereinafter called time of exposure.
  • a saw tooth potential which is generated by the device lll and. serves to deflect the beam of cathode rays in a direction parallel with the scanning lines, the period of which determines the scanning time of one scanning line.
  • a non-modulated oscillation which is generated by the oscillator 24 whose frequency is preferably a multiple of the saw tooth potential generated by the device l0
  • the movement of the scanning beam in scanning each scanning line will be accelerated and retarded during each half cycle of the impressed oscillation.
  • the total scanning time of a scanning line remains constant and equal to the period of the saw tooth potential generated by the device I 0. 10
  • the time during which the electrons strike the screen is inversely proportional to the speed at which the scanning beam moves over the screen. During that part of the half cycle of the impressed oscillation, in which the movement of the scanning beam is accelerated, the time during which the electrons strike the screen is short, and during the retarded part of the half cycle of the impressed oscillation the time of exposure is long. If the curve indicating the quantity of light L emitted under bombardment by electrons as a function of the time T has the shape illustrated in Figure then the emitted quantity of light increases with an increase of the time of exposure from the value T1 to T2, i.
  • the acceleration and the retardation of the beam of cathode rays during each half cycle of the impressed oscillations increases and decreases respectively in accordance with the increase and .clecrease respectively of the amplitude of thei oscillations; in other words the average quantity of light emitted during each cycle of the oscillations impressed on the deflecting plates 8 varies in accordance with the amplitude of these oscillations since the increase of the quantity of light;.- emitted during that part of the half cycle of the impressed oscillations, in which the scanning beam is retarded, is always appreciably larger than the decrease during that part of the half c 'cle in which the scanning beam is accelerated
  • the amplitude of the oscillations supplied to the deflecting plate 8 varies in accordance with the low frequency picture currents'which are modulated on said oscillations so that a variation
  • the time during which the electrons strike the screen is inversely proportional to the velocity with which the screen is scanned. With a bright picture element the time during which the electrons strike the screen is long and with a dark picture element'the time of exposure is short or vice versa. If the curve which represents the quantity of light L which is radiated upon electron bombardment as a function of the time of exposure has a shape as shown in Figure 3, the quantity of light emitted increases, with an increase of the time of exposure from the value T1 to T2, that is to say during the reproduction of a bright picture element, more strongly than the quantity of light emitted decreases, due to the decrease of the time of exposure from T1 to T3, during the reproduction of a dark picture element.
  • the amplitude of the carrier wave fed to the deflecting the quantity of light emitted decreases more than proportionally with time. In either case the contrasts betweenthe light and dark picture elements are also increased, whereas the average quantity of light emitted is larger than when using a television receiving arrangement not in accordance with this invention, in which the lowfrequency picture currents control the intensity of the beam of cathode rays.
  • electrostatic deflection means any form of deflection, whether electrostatic, electrodynamic, or a combination of these, may be used.
  • a television receiving arrangement comprising a cathode ray tube, means for producing a cathode ray beam in the tube, a screen adapted to emit light when subjected to electronic bombardment and having the property that a nonlinear relationship exists between the time during which the electrons strike the screen and the quantity of light emitted therefrom, means for deflecting the cathode raybeam inone direction at a constant frequency, means for generating a substantially high frequency carrier wave, means for modulating the carrier wave by the received picture signals, and means for very rapidly varying the rate of deflection in accordance with the intensity of the modulated carrier wave.
  • a television receiving arrangement comprising a cathode ray tube, means for producing a stream of electrons in said tube, said tube includ ing a screen adapted to emit light when bombarded by the stream of electrons and which has the property that a non-linear relationship exists between the time during which the electrons strike the screen and the quantity of light emitted-thereby, means for repeatedly deflecting the beam of electrons in substantially perpendicular directions at different constant frequencies to scan said screen, means for rapidly accelerating and decelerating the rate of deflection of the beam in one direction at a constant rate, and means for controlling the amount of acceleration or deceleration in accordance with the received picture signals.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Details Of Television Scanning (AREA)
US168122A 1936-11-09 1937-10-09 Television receiving system Expired - Lifetime US2193857A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NL2193857X 1936-11-09

Publications (1)

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US2193857A true US2193857A (en) 1940-03-19

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US168122A Expired - Lifetime US2193857A (en) 1936-11-09 1937-10-09 Television receiving system

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US (1) US2193857A (enrdf_load_stackoverflow)
BE (1) BE424502A (enrdf_load_stackoverflow)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2597054A (en) * 1942-11-17 1952-05-20 Cfcmug Coupling for cathode-ray tubes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2597054A (en) * 1942-11-17 1952-05-20 Cfcmug Coupling for cathode-ray tubes

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Publication number Publication date
BE424502A (enrdf_load_stackoverflow)

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