US2109618A - Television system - Google Patents

Television system Download PDF

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Publication number
US2109618A
US2109618A US700478A US70047833A US2109618A US 2109618 A US2109618 A US 2109618A US 700478 A US700478 A US 700478A US 70047833 A US70047833 A US 70047833A US 2109618 A US2109618 A US 2109618A
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US
United States
Prior art keywords
signals
picture
synchronizing
amplitude
channel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US700478A
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English (en)
Inventor
Ralph S Holmes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
RCA Corp
Original Assignee
RCA Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to BE406509D priority Critical patent/BE406509A/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US700478A priority patent/US2109618A/en
Priority to FR781668D priority patent/FR781668A/fr
Application granted granted Critical
Publication of US2109618A publication Critical patent/US2109618A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/44—Receiver circuitry for the reception of television signals according to analogue transmission standards
    • H04N5/52—Automatic gain control
    • H04N5/53—Keyed automatic gain control

Definitions

  • My invention relates to improvements in television systems.
  • the eiect of the variations referred to is manifested at the receiver by wide variations in the overall brilliancy of the received picture and, possibly, by overloading of the ampliilers.
  • the intercepted picture and synchronizing signals, transmitted together on a carrier wave as modulations thereof, are passed through an electrical channel which supplies the scanning apparatus.
  • the synchronizing signals are taken from this channel. at a point therein where they are of suillcient amplitude and of the right polarity, and are rectied to develop an electrical potential the amplitude of which varies proportionally with occurring variations in the effective amplitude of the synchronizing signals.
  • the electrical potential so developed is applied to one or more control circuits in the electrical receiving channel, and is effective to decrease the sensitivity of the latter when the signal level tends to rise and to increase such sensitivity when the signal level tends to drop.
  • My invention resides in the improved system and method of operation of the character here- 'inafter described and claimed.
  • Figure 1 is a diagrammatic view of a television receiving system including a preferred embodiment of my invention
  • Fig. 2 is a graphical illustration of the principle of operation in Fig. 1;
  • Fig. 3 is a diagrammatic View of an amplifier stage
  • Fig. 4 is a diagrammatic view, showing a modiiication of the system in Fig. 1.
  • the numeral III designates scanning apparatus for developing an image of the transmitted subject.
  • This apparatus is shown as being in the form f a cathode ray tube I2 provided with a gun I4 for developing a ray I6 o! electrons and directing the same at a iluorescent screen I8 on which the transmitted picture is reproduced.
  • a plurality of electromagnetic coils 20 are provided, that operate to deilect the ray 43,20 times a second horizontally, and a plurality of electromagnetic coils 22 that operate to deflect the ray simultaneously 24 times a second vertically.
  • a suitable generator 24 operates to develop a saw-tooth current wave at 4320 cycles and to cause this wave to pass through the coils 20, while a suitable generator 26 operates to develop a saw-tooth current wave at 24 cycles and to cause this wave to pass through the coils 22.
  • the picture signals are applied to a control grid 28 forming part of the gun I4, whereby the intensity of the ray I6 is made tovary directly proportionally with occurring variations in the picture signals.
  • a source 29 of anode potential is provided, and adjustment of potentiometer 30 determines the positive potential applied to the rst anode 32.
  • a synchronizing signal or impulse is developed by suitable ap- I paratus operating independently of the apparatus for developing the picture signals but synchronous with it. 'I'he synchronizing signals, therefore, occur at the rate of 4320 a second, and during the periods t, when there are no plcture signals. 'There are also developed, with the synchronizing signals, other control signals, indicated at 40 in Fig. 2, where are termed framing signals and occur at the rate of 24 a second.
  • the framing signals have the same amplitude as the synchronizing signals, but are of substantially greater duration than the latter.
  • the connections and operating action are such that the polarity of the picture signals, representative of conditions of light at the transmitted subject, is opposite to the polarity of the synchronizing and framing signals, as indicated in Fig. 2.
  • the picture signals and the synchronizing and framing signals, transmitted together on a carrier Wave as modulations thereof, are intercepted by an electrical channel A, having at'its input end aradio-frequency, alternating current amplifier 42.
  • 'I'he incoming lcarrier wave is demodulated to a lower, intermediate frequency by a detector 44 and an associated local oscillator 46.
  • the beat wave, at the intermediate frequency is amplified by an intermediate frequency amplifier 48.
  • 'I'he beat wave is then rectified by a second detector 50 at the output end of the channel A, to obtain the signal wave which is amplified by a low frequency amplifier 52 supplied from the second detector.
  • the signal wave and the polarities are as represented in Fig. 2, with the synchronizing signals in the black direction and of positive polarity.
  • the synchronizing and framing signals operate to drive the generators 24 and 26, respectively.
  • the generator 24 begins a new cycle of its operation with the occurrence of each synchronizing signal.
  • the generator 26, in like manner, begins a new cycle of its operation upon the occurrence of each framing signal, and this generator is so constructed and adjusted that it will not respond to the synchronizing signals which are of substantially shorter duration than the framing signals.
  • the construction and adjustment of the generators 24 and 26 is such that they are not affected by the peak picture signals, but only by the control signals of greater amplitude.
  • 'I'he signal wave as represented in Fig 2, is applied by the connection 56 to the input of the picture signal circuit 58. From the output of this circuit, the picture signals representative of conditions of light on the transmitted subject are of positive polarity, and the synchronizing and framing signals are of negative polarity.
  • 'I'hese signals are applied as indicated to the grid 28 of the tube I2. 'I'he amplitude of these signals is sufficiently high to completely cut 01T the ray I6 during return deflection thereof in the horizontal and vertical directions.
  • the signal wave is supplied by the connection 56 to the grid circuit of a plate circuit detector 60.
  • 'I'he peak amplitude :t of the synchronizing signals is a measure of, or is proportional to the strength of the incoming signals. This condition is utilized to vary the plate current of the tube 60 automatically and substantially proportional to variations in the signal strength. The result is that across a resistor 59 in the output or plate circuit of the tube 60, an electrical potential is developed whose amplitude varies substantially proportionally with occurring variations in the amplitude :c of the synchronizing signals.
  • the anode end of the resistor becomes more negative with an in-l crease in .'c, and when :c decreases it becomes correspondingly less negative.
  • the electrical potential so developed is applied to the grid circuit of one or more of the stages of the intermediate frequency amplier 48, as indicated by the connections 64 and as shown in Fig. 3. As the electrical potential becomes more negative, the sensitivity of the electrical channel is decreased correspondingly, and as the potential becomes less negative, the sensitivity of the channel is increased correspondingly. In this manner, the level of the signals applied to the scanning apparatus I is maintained substantially constant.
  • the negative control potential developed in the plate circuit of the tube 60 may be applied to the grid circuit of one or more stages of the radio frequency amplifier 42, as indicated by the broken lines 66.
  • a potential source 61 is provided, the positive terminal of which is connected to ground and the negative terminal of which is connected to the cathode end of the output resistor 56.
  • the signal amplitude at which the control becomes effective may be determined.
  • the picture and synchronizing signals are fed directly to the picture signal circuit 58 from the low frequency amplifier 52, as in Fig. 1.
  • the signals as represented in Fig. 2 are first taken from the low frequency amplifier 52 and passed through an auxiliary amplifier 1l of a conventional design to pass only the synchronizing and framing signals in Fig. 2, rejecting the picture signals of opposite polarity.
  • the ampliiler supplies a suitable form of separating circuit 12 which operates to separate the synchronizing and framing signals, so that in the output connection 14 from this circuit there will appear only the synchronizing signals, and in the output connection 16 there will appear only the framing signals.
  • the generator 24 is, therefore, supplied only with synchronizing signals by the connection 14, andthe generator 26 is supplied only with framing signals by the connection 16.
  • the control signals for the input circuit of the tube 60 can be supplied from the connection 18, or from the connection 80, or from either of the connections 14 and 16. In doing this, it will be understood that the conditions of polarity must be correct so that the desired control of sensitivity of the channel A is obtained.
  • tube 80 it will be understood that other known devices, such as a diode or a gridleak rectier, can be used for the same purpose, in which case consideration will be given for the correct conditions of polarity of the signals supplied to the rectier device, as will be well understood.
  • a diode or a gridleak rectier can be used for the same purpose, in which case consideration will be given for the correct conditions of polarity of the signals supplied to the rectier device, as will be well understood.
  • a television receiving system apparatus for developing an image of the transmitted subject, an electrical channel for intercepting picture signals and synchronizing signals transmitted together on a carrier wave as modulations thereof, a rectifier at the output end of said channel, an amplifier supplied from said rectifier and operating to supply said apparatus directly with picture signals and synchronizing signals, the picture signals representative of conditions of light at the transmitted subject being of opposite polarity both to the synchronizing signals and to the picture signals representative of conditions of shade at the transmitted subject, means supplied from said amplifier for developing an electrical potential whose amplitude variesin response to and in accordance with occurring variations in the effective amplitude of the synchronizing signals, and connecting means for applying such electrical potential to an operating circuit in said channel effective to control the sensitivity of said channel in accordance with occurring variations in amplitude of the applied potential.
  • the method of operation Which comprises transmitting picture signals and synchronizing signals together on a carrier wave as modulations thereof and under conditions such that the picture signals representative of conditions of light at the transmitted subject are of opposite polarity both to the synchronizing signals and to the picture signals representative of conditions of shade at the transmitted subject, utilizing the received synchronizing signals to develop an electrical potential whose amplitude varies in response to and in accordance with occurring variations in the effective amplitude of the synchronizing signals, and applying the developed electrical potential to the receiving apparatus to vary the sensitivity thereof in the sense that an increase in the amplitude of the received synchronizing signals causes a decrease in the sensitivity of said apparatus and a decrease in the amplitude of the received synchronizing signals causes an increase in the sensitivity of said apparatus.
  • apparatus for developing an image of the transmitted subject, an electrical channel for intercepting picture signals and synchronizing signals transmitted together on a carrier wave as modulations thereof;
  • said channel comprising an amplifier at the input end thereof, a detector supplied from said amplifler, a second amplifier supplied from said detector, and a second detector supplied from said second amplifier; a third amplifier supplied from said second detector and operating to supply picture and synchronizing signals directly to said apparatus under conditions such that the picture signals representative of conditions of light at the transmitted subject are of opposite polarity both to the synchronizing signals and to the picture signals representative of conditions of shade at the transmitted subject, means supplied from said third amplifier and operating to develop an electrical potential of negative polarity which becomes more negative upon an increase in the effective amplitude of the synchronizing signals and which becomes less negative upon a decrease in such amplitude, and connecting means for applying such electrical potential to at least one control circuit in said channel effective to vary the sensitivity of the latten 4.
  • a cathode ray tube for developing an image of the transmitted subject and provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, means for causing the ray to scan a given area of said screen and comprising means for deflecting the ray in a given direction at a given frequency, an electrical channel for intercepting picture signals and control signals transmitted together on a carrier Wave as modulations thereof, means supplied with picture signals from said channel and operating to vary the intensity of said ray in accordance with occurring variations in such signals, said ray-deflecting means being supplied with the control signals from said channel and being maintained thereby in operation at said frequency, means supplied from said channel with an electrical wave comprising the picture and control signals for developing an electrical effect which becomes more negative in response to an increase in the effective amplitude of the control signals and which becomes less negative in response to a decrease in such amplitude, and connecting means for applying such electrical effect to at least one control circuit in said channel effective to vary the sensitivity of the latter.
  • a cathode ray tube for developing an image of the transmitted subject and provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, means for causing the ray to scan a given area of said screen and comprising means for deecting the ray in a given direction at a given frequency, an electrode for Varying the intensity of the ray, an electrical channel for intercepting picture signals and control signals transmitted together on a carrier wave as modulations thereof; said channel comprising an amplifier at the input end thereof, a detector supplied from said amplifier.
  • a second amplifier supplied from said detector, and a second detector supplied from said second amplifier; a third amplifier supplied from said second detector and operating to supply the picture and control signals to said electrode under conditions such that the picture signals representative of conditions of light at the transmitted subject are of opposite polarity both to the control signals and to the picture signals representative of conditions of shade at the transmitted subject, means supplied from said third amplier and operating to develop an electrical eiect which becomes more negative upon an increase in the effective amplitude of the control signals and which becomes less negative upon a decrease in such amplitude, and connecting means for applying such electrical eiect to at least one control circuit in said channel eiective to vary the sensitivity of the latter.
  • a receiver comprising an electrical discharge device having a control electrode, means for deriving a unidirectional control voltage from ⁇ said composite signal which voltage varies substantially in accordance with the amplitude of said synchronizing signals as measured from said axis, means for applying said control voltage to said control electrode whereby the operation of said electric discharge device iscontrolled in accordance with rthe amplitude of said synchronizing signals, and
  • a receiver comprising a signal channel including an amplier for amplifying a carrier modulated by said composite signal and a detector located at a later point in said channel for reproducing said composite signal, said ampliiler including a gain control means, means for deriving a uni-directional control voltage from

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Picture Signal Circuits (AREA)
US700478A 1933-12-01 1933-12-01 Television system Expired - Lifetime US2109618A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
BE406509D BE406509A (xx) 1933-12-01
US700478A US2109618A (en) 1933-12-01 1933-12-01 Television system
FR781668D FR781668A (fr) 1933-12-01 1934-11-22 Perfectionnements aux systèmes de télévision

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US700478A US2109618A (en) 1933-12-01 1933-12-01 Television system

Publications (1)

Publication Number Publication Date
US2109618A true US2109618A (en) 1938-03-01

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Family Applications (1)

Application Number Title Priority Date Filing Date
US700478A Expired - Lifetime US2109618A (en) 1933-12-01 1933-12-01 Television system

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US (1) US2109618A (xx)
BE (1) BE406509A (xx)
FR (1) FR781668A (xx)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE752761C (de) * 1935-11-02 1954-02-08 Telefunken Gmbh Verfahren zur Schwundregelung der Ausgangsamplitude des Verstaerkers fuer den Empfang von Fernsehsendungen

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Publication number Publication date
BE406509A (xx)
FR781668A (fr) 1935-05-20

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