US2310285A

US2310285A - Television transmitting system

Info

Publication number: US2310285A
Application number: US412920A
Authority: US
Inventors: Oscar B Hanson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1941-09-30
Filing date: 1941-09-30
Publication date: 1943-02-09
Anticipated expiration: 1960-02-09

Description

Feb. 9, 1943. I o. HANSON 2,310,285

TELEVISION TRANSMITTING SYSTEM Filed Sept. 50, 1941 JZZwZzb Labhic awsde,

INVENTOR ATTO RN EY Patented Feb. 9, 1943 UNITED STATE TELEVISION TRANSMITTING SY STM Oscar '8. Hanson, WestporhConn assignor to America, a corporation of Radio Corporation of Delaware Application September 30,1941, Serial No. 412,920

11 Claims. (CL 178-71) The present invention relates to a television transmitting system and, more particularly, to systems wherein the television field or frame frequency does not bear a harmonic or a sub-har monic relationship to the power line frequency.

In present television systems an optical image of the object or scene to be transmitted is proiected upon the light responsive electrode and the television camera. An electrical charge ima e. is produced on the electrode as a result of the variations in the light intensity of the optical image and the light responsive electrode or some other electrode bearing a charge image is scanned by a focused cathode ray beam in order to produce a series of picture signals. For the scanning operation the cathode ray beam is deflected in mutually perpendicular directions at different related rates in. order that the charge image of the light responsive electrode may be scanned in a systematic manner.

When the television camera is used in an indoor studio, artificial lighting must, of;course be now distributed at 60 cycles alternating current, then naturally the sources of studio lighting are energized'from the 60 cycle power. In virtually all lighting devices which operate on a 60 cycle exist a considerable variation in light. intensity and the light intensity will fluctuate at the rate of 120 fluctuations per second (for-single phase operation).

If the television transmitting tube is operated .in such a manner that the scanning "rate in flelds per second corresponds" to, or 'is a multiple or sub-multiple of the power line frequency, then this variation in light intensity in the studio is not particularly objectionable, since the variation foreach'successive field or frame remains relatively constant and fixed in position with respect to any particular portion ofthe picture area. Variation in brilliancy of the illumination source will naturally cause a variation in signalstrength, but this variation in signal strength may be removed or' compensatedfor in the. dark spot correction circuit which is normally provided in television transmitting sysused, and inasmuch as mostelectrical power is tems. By an adjustment of the dark spot correcting network the variation in picture signal strength may be compensated for and the spurious signals may be effectively removed.

If, however, the. deflection rate or scanning rate at which the television camera is operated does not bear a harmonic or sub-harmonic relationship to the frequency of the alternating current power line, then the variations in light intensity in the. studio are quite objectionable and, unless removed, appear as'light and dark horizontal bands that move vertically across the receiver screen. The rate of progressive or retrogressive movement is naturally a function of the. relative frequencies at which the television fields repeat, as compared with the power line current alternations.

One purpose of the present invention, therefore, is the provision of the means and apparatus whereby spurious-signals which are introduced into the video signal series may be compensated.

' rate corresponding to twice the power line ire-- quency so that the video or picture signals vary in intensity in accordance with the pulsations in the light emitted from the studio light sources.

' Another'spurioussignal whichis introduced in I the video signal series is the double power line frequency signal component, which naturally must beremoved from the video signal series.

This spurious signal is also at double the power line frequency and inasmuch as the video signal megacycles per second or higher, naturally the double power line frequencies, which are introduced by reason of the variable intensity light source, are transmitted along with the actual picture signals.

Another purpose of the present invention,

' therefore, resides'in the provision of means whereby the undesired amplitude modulation of the picture signals may be removed.

Still another purpose of the present invention resides in the-provision of means whereby the spurious double power line frequency signals a may be removed from the picture signal series.

tubes for the picture signal series may be varied at double the power line frequency in order to compensate for the undesired amplitude modulation of the picture si nals. 7

- Still other and advantages of the present invention will become more app rent to those skilled in the art from the following speciilcation and claims, particularly when considered in connection with the drawing wherein:

Figure 1 schematically represents one form of the present invention and.

Figure 2 shows a curve representing the opersides in the provision of means whereby the gain or amplification factor of one of the amplifying ating characteristic of a picture signal amplifvin: tube.

- Referring now to the dr wing, and particular ly'to Figure 1, a television transmitting camera is shown schematically at ll and the camera necessarily includes a television transmitting tube, together with a lens system for, projecting an optical image of the 'subiect matter or scene to'be transmitted upon a light responsive electrode'in the television transmitter, tube. -The camera also includes means for scanning an electrical'charge image-representative of the optical image in order to produce a picture signal series which is applie'dto the 'output-conductor ll of the television camera.

-- A studio lighting source it is also shown and the. light source is energized from the alternatin 'current power line. The studio lighting source naturally is used to provide the desired illumination in order that-a sufficiently intense optical image may be projected upon the light responsive electrode in the television transmitting tube.

-' A picture signal ampliiier'tube l8-is provided including at least a cathode,.a'control electrode,

and an anode. This picture signal amplifier;

tube may have an operatlngcharacteristic as indicated in Figure'2 'of-thedrawlng and preferably the intensity" of the picture signals which are applied to the control electrode of tube Ii, by way of condenser ll,-ls so regulated that the peak to peak'picture signal voltagewill be small as compared to the total operating range represented at 'O-X in Figure 2. In order to maintain the anodebf hibe I! positive with respect to its cathode,- a source of positivepotential is applied to theterminal "20 and connected between the terminal "(and the anode of the tube is a load 22. .lwnsn the picture signals are applied to the ,controlelectrode' of tube it, they will be. amplified-by. the tube and these ampliiled signals may be derived from the output conductor 24.

In the system asso iardescribed; no compensation for variations in studio light intensity has beenma'ds and when the television camera is operated asynchronously with respect to the power line frequency, the-spurious signals which would be present in conductor 2! would seri-. 75'" y way of coupling condenser N we cusly impair the quality of the reproduced image in many practical cases.

In order to compensate for the undesired signals which are introduced by reason of asynchro nous operation of the television camera a phototube 25 is provided. This photo-tube or light responsive tube is positioned in the studio and preferably relatively-, .ad,iacent the television camera in order that the light which is permitted to strike the photo-cathode of the phototube is substantially the same as the light which is used in the television transmitting camera. Accordingly, the output from the photo-tube will bear a direct relationship to the fluctuations in light intensity of the studio light source II. In- 1 asmuch as the fluctuations of the produced light in most cases will not vary sinusoidally or will not correspond to the wave form of the power line frequency, it is'desirable to derive correction control potentials from the photocell 25. The variations in potentials which are derived from the photo-tube and which are a result ofthe variations in the studio lighting are applied In order that'both negative and positive co'ntrol potentials may be derived from tube 28 and inorder that their intensity may be controlled, two potentiometers 32 and 34 are provided. A point 36 along the potentiometer 32 is connected to ground or a point of fixed potential, and a corresponding point 38 on potentiometerrfl'is also'connected to the same point of hired peten-' tiai. Cooperating with potentiometers 32 and-34: I

are movable contacts 40 and 42 respectively;

A tube 44 is providedwhich includes, a cathode,

a control electrode and an anode: :Theicath'ode is connected to ground or a point of fixed 'poten-- tial through cathode resistance Brand the con trol electrode is also connected to ground throughthe grid resistance 48. The movable contact 40 of the potentiometer 32 is connected to the con-'-- trol electrode of tube 44 by way of condenser ill in order that the voltage variations which appear along potentiometer 32 may be applied between the control electrode of tube 44 and its associated cathode. .The anode of tube 44 is maintained positive with respect to its cathode by connecting a loadrresistance'52 between the positive termine] 20 and the anode of the tube. The voltage variations which are derived-from the phototube 25 will have a frequency of double the power grid resistors 54 and (as well as biased cell or the grid biasing potential 58. The voltage variations which appear at the'anode of tube 44 are applied to the junction of grid resistors 54 and signal ain-v plifler tube It is connected to ground through the trode and an anode.

- potentiometer "a it'ispoesible,

' coupling condenser II and resistance It and to the control electrode of tube ll, therefore alter thezoperation point of the tube It alongits'characterlstic curve. when the potential of the con- .trol electrode of tube I I is reduced or altered in a negative direction, it-operatesjin a range near-' er the point X, whereas when the potential of the control electrode of tube. It is altered in a positive direction,- then the-tube wiil"oper ate about a point on the characteristic curve nearer the point '0. This" shifting of the, operating range of tube it along "its'characteristic curve naturally altersthe gain of the tube so that it is effective to amplify the picture signals in varying amounts in accordance with its rangc of operation along its characteristic curve. As stated above, picture signals, as derived directly from the television camera are amplitude modulated at double the power line'frequency, and, by altering the gain'of tube ll (by'varying its bias) this undesired amplitude modulation maybe removed. substantially-completegremoval of this undesired amplitude modulation is accomplished by-properly adiustingthemovable contact 40 along the potentiometer 3!. Furthermore, inasmuch as the photo-tube II responds to fluctuations in lightproduced by the studio lighting "source and since'the' undesiredamplitude inodu- -lation of the video signals is also a function of the fluctuations in'the studio lighting, substanulation may be accomplished by the above described method and bpl aratusu There yet remains a, further undesired spurious tube it which are comparable in frequency and in intensity to the undesired-voltage variations ent in the picture signals as finally transmitted.

. Accortiiuglyfthe und'uired lightand dark-vertically moving horizontal bands which would otherwise be visible in the receiver are eliminated. It ispossible, therefore, to derive from the output conductor 24 a picture signal series which is properly indicative ofthe scene or optical image televised and which does not include any spurious signals or undesired amplitude modulations as a result of fluctuations in the studio lighting whenthe television camera is operated asynchronously with respect tothe power line frequency. w

The system is readily adaptable to any type television camera and may be used to remove the undesired spurious signals, as well as the undesired amplitude modulation of the picture signals. Furthermore, the system is read ly adaptable to any type studio lighting, since the photocell I! responds directly to fluctuations in the light supplied in the studio.

- Various alterations and modifications may be made in the present invention without departing tial complete elimination of the undesired-mod- This is accomplished by the'provision of tube 82' which includes at least i cathode. a control elec- The cathode 'and the consignal of double thepower line frequency which 5 must be removed from the video signal series trol electrode of this tube are connected to 0 ground or a point-of fixed potential through cathode and control resistances 84 and It. re-

- yspectively, and the control electrode of tube Ii is also connected to the movable contact 42 of the potentiometer N by means'of condenser 68. 'Ihere is, therefore, a voltage variation impressed upon" the control electrode oftube 82 which is determined in intensity and polarity by. the posi- Qtion of the movable contact-sllwith res ect to theground point 38. The" wave form. of these voltage variation corresponds substantially identically to the variation in the light'in the studio.

' The anode of tube 02 is connecteddirectly to the anode of tube It inaorder that a positive poten tial may beap'plied-tothe anode of -tube vO2 with respect'to its associated cathode. Furthermore; by reason of connection, voltage variations I which appear at the ,anode of tube 02 are also superimposed upon the voltage variation appearing in the anode circuit of tube It. Theload resistance for tube ll is the'resi'stance' l2,- which is commonto-both tubes "and I. By an adiustment'of the; movable contact I along the thereforeJto-sufrom the spirit and scope thereof, and it is desired that any and all such modifications be considered within the-purview of the present in vention, except as limited by the hereinafter appended claims.

What I claim is:

1. A circuit arrangement for use in a television transmitter wherein artificial lighting is employed and wherein the source of artificial light is energised from an alternating current power line having a frequency difierent from the television field scanning frequency comprising a light responsive element for producing voltage variations in accordance with the fluctuations in the artificial'lighting, a television camera for producing a series of video signals,'means including an amplifier tube for amplifying the video signals, and means for altering the amplification factor of said video signal amplifying tube in accordance with the voltage variation; derived from the Iight responsiveelement to compen-- sate for cyclically recurrent changes in the intensity of the produced video signals.

2; A circuit arrangement for use in a television transmitter wherein artificial lighting is employed and'wherein the source of artificial light is energized from an alternating current power line having a'f'frequency different from the television field scanning frequency comprising a television camera for producing a series of video signals, means including an amplifier tube" for amplifying the video signals, a light responsive tube for producing valtage variations in accordance with the fluctuations in the artificial lighting, means for amplifying the produced voltage varia- 'tions, and-means for altering the amplification factor of said video signal amplifv s tube in accordance with the amplified voltage variations to compensate for'cyclically recurrent changes in the intensity of the produced video signals.

perimpose voltage variations upon the anode of 7s 3. A television transmitting system including an artificial light source, means for energizing the light source from an alternating current power line having a predetermined frequency, a

television camera for producing a video signal series, the field repetition rate at which a scene of action is scanned by the camera being different from the said predetermined frequency of the alternating current power line, means for amplifying the video signal series, a light responsive tube positioned to respond to variations in the artificial light, and means for superimposing the voltage variations derived from the light responsive tube upon theamplified video signal series to thereby eliminate cyclically recurrent transient signals from the video signal series.

4'. A television transmitting system ,including a source of artificial light, means for energizing the 1 light source from an alternating current power line having a predetermined frequency, a I

television camera for producing a video signal seris,,the television fieldrep'etition rate at which a scene of action is scanned by the camera bein different from the said predetermined frequency of the alternating current power line, means for I the artificial light maybe compensated.

5. A television transmitting system including an artificial light source, means forenergizing the light source from an alternating current power line having "a predetermined frequency, a television camera for producing a television picture signal series, the field repetition rate at which a scene of action is scanned by the'camera being different from the saidpredetermined fre- "queney of the alternating current power line,

means for amplifying the picture signal series, a light responsive cell positioned relatively adjacent the camera to respond to variation in the artificial light and for generating voltage variations in accordance with the light variations, means for superimposing the voltage variations derived from the light responsive cell upon the amplified video signal series, and a single means I light responsive tube positioned to respond to for controlling the amplitude and polarity of the* superimposed voltage variations in order that cyclically recurrent spurious signals resulting from fluctuations in. the artificial light may be compensated.

6,. In a television transmitting system wherein artificial lighting is used, the artificial light sources being energized from an alternating current'power line, and wherein the television field repetition rate is different from the frequency of the alternating current power line comprising a .said'light responsive cell to compensate for cyclically recurrent amplitude modulations of the picture signal series as a result. otthe asynchronous operation of the television camera as compared with the frequency of the alternating.

current power line. I

7. In a television transmitting system wherein Y the alternating current power line comprising a light responsive tube positioned to respond to fluctuations in the artificial light source, a television camera for producing a series of picture signals, an amplifier tube for amplifying the series of picture signals, means for varying the amplification factor of the amplifying tube in accordance with voltage variations derived from said light responsive tube, and means responsive v to the voltage variations from said light respon- 8. Ida television transmitting system wherein. artificial lighting is used, the artificial light sources being energized from an alternating .cur-

rent power line, and wherein the television field repetition rate is different from the frequency of the alternating current power line comprising a fluctuations in the artificial light source for generating voltage variations corresponding to the light fluctuations, a television camera for producing a"series of picture signals, an amplifier tubefor amplifying the picture signals, means for varying the amplification factor of the amplifying tube in accordance with the generated voltage variations, and means responsive to the with the frequency. the alternating current power line used 'to' energize the artificial light sources. i

' 9. In a televisiontransmitting system wherein artificial light is used in the studio and wherein" the television camera is operated asynchronously with respect to the frequency of the alternating current power line used to energize the artificial light.source,yincluding a television camera for producing a series of picture signals, an amplifying tube for increasing the intensity of the series of picture signals, a light responsive cell posi-.-

tioned to respond to fluctuation in the artificial light, and means responsive to the voltage variations derivedfrom the light responsive cell for varying the amplification factor of the amplifying tube, in order that cyclically recurrent amplitude modulations of the picture signals by reason of the asynchronous operation of the television camera may be substantially completely eliminated. v r

10. In a television transmitting system where- .in artificial light is used in the studio and wherein the television camera is' operated asynchronously with respect to the frequency of the alternating current power line used to energize the artificial light source, including a television camera for producing a series of picture signals, an

qua-1,090

amplifying tube for increasing the intensity of the series of picture signals, a light responsive tube positioned tov respond to fluctuation inthe artificial light, means responsive to the voltage variations derived from the light responsive tube for varying the amplification factor of the amplitying tube, and means for superimposing a predetermined component of the voltage variations derived from the light responsive tube upon the amplified series of picture signals, the predetermined component being adjustable as to intensity and polarity relationship in order that cyclically recurrent spurious signals introduced in the series of picture signals by reason of the asynchronous operation of the television camera may be substantially com'pletely compensated.

ii. In a television transmitting system wherein artificial light is used and wherein the television camera is operated asynchronously with respect to the frequency of the alternating current power line used to energize the artificial light source, including a television camera for producing a series of picture signals, an amplifying tube for increasing the intensity of the series of picture signals, a light responsive tube positioned to respond to fluctuation in the artificial light source for generating voltage variations inaccordance with the light fluctuations, means responsive to'the voltage variations derived from the light responsive tube for varying the amplification factor of the amplifying tube within predetermined adjustable limits, and means i for superimposing a predetermined component of the voltage variations derived from the light responsive tube upon the amplified series of picture signals, the predetermined component being adjustable as to intensity and polarity relationship in order that cyclically recurrent spurious signals introduced in the series of picture signals by reason of the asynchronous operation of the television camera may be substantialLv completely compensated.

OSCAR B. HANSON.