Патент USA US2109618код для вставки
March 1, 1938. R. s. HOLMES TELEVISION SYSTEM Filed Deo. l, 1935 ' 2,109,618v 2,109,618 Patented Mar. 1, 1938 UNITED STATES -PATENT OFFICE 2,109,618 TELEVISION SYSTEM Ralph S. Holmes, Haddonñeld, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December l, 1933, Serial No. 700,478 7 Claims. i) My invention relates to improvements in tele vision systems. In communication by television, wherein pic ture signals and synchronizing signals are inter cepted and supplied to some form of scanning apparatus which develops an image of the view at a particular transmitting station, there occur variations over a substantial range in the ampli tude or level of the received signals. These varia il) tions occur, for example, upon tuning the receiv ing apparatus for reception from different trans mitting stations of different power and/or dif ferent distances from the receiving apparatus. Such variations, also, are attributed to atmos ' pheric disturbances and the phenomenon com monly referred to as “fading”. The eiïect of the variations referred to is mani fested at the receiver by wide variations in the overall brilliancy of the received picture and, 20 possibly, by overloading of the ampliilers. With the foregoing in mind, it is one of the objects of my invention to provide an improved television system wherein provision is made for automatic control or adjustment of the same in vision receiving system including a preferred em bodiment 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; and Fig. 4 is a diagrammatic view, showing a modi iication of the system in Fig. 1. With reference to Fig. 1, the numeral III desig nates scanning apparatus for developing an im age of the transmitted subject. This apparatus is shown as being in the form òf 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. Assuming that there are to be 24 frames a second, each frame to have 180 lines horizontally, a plurality of electromagnetic coils 20 are provided, that operate to deilect the ray 43,20 times a second horizontally, and a plu 20 rality of electromagnetic coils 22 that operate to deflect the ray simultaneously 24 times a second vertically. For this purpose, a suitable generator 24 operates to develop a saw-tooth current wave 25 such manner that the amplitude or level of the at 4320 cycles and to cause this wave to pass picture and synchronizing signals supplied to the scanning apparatus is maintained substantially through the coils 20, while a suitable generator constant. Other objects and advantagesv will hereinafter 30 appear. .. In accordance with my invention, the inter 26 operates to develop a saw-tooth current wave at 24 cycles and to cause this wave to pass through the coils 22. Operating action of the scanning apparatus is 30 maintained in synchronism with that at f the mitted together on a carrier wave as modulations transmitter by synchronizing or control signals eñective to drive the generators 24 and 26, as will thereof, are passed through an electrical channel hereinafter more fully appear. cepted picture and synchronizing signals, trans 35 which supplies the scanning apparatus. The syn chronizing signals are taken from this channel. at a point therein where they are of suillcient amplitude and of the right polarity, and are rectiñed to develop an electrical potential the 40 amplitude of which varies proportionally with occurring variations in the effective amplitude of the synchronizing signals. The electrical poten tial so developed is applied to one or more control circuits in the electrical receiving channel, and 45 is effective to decrease the sensitivity of the lat ter when the signal level tends to rise and to in crease such sensitivity when the signal level tends to drop. My invention resides in the improved system 50 and method of operation of the character here 'inafter described and claimed. For the purpose ol' illustrating my invention, an embodiment thereof is shown in the drawing, wherein Figure 1 is a diagrammatic view of a tele , ._ With regard to the various details of construc tion in Fig. 1, these are assumed to be comparable to those disclosed in the copending application by Arthur W. Vance, filed June 17, 1931 and bearing Serial No. 544,959. For the purpose of reproducing the transmitted picture on the screen I8, 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 occur ring variations in the picture signals. A source 45 29 of anode potential is provided, and adjustment of potentiometer 30 determines the positive po tential applied to the ñrst anode 32. For the purpose of illustration, it shall be as sumed that at the transmitter the object or pic 50 ture is scanned to cause variation of current in ` the output circuit of some form of photosensitive apparatus, whereby picture signals in the form of a current wave are developed, as indicated at 34 in Fig. 2. Scanning action at the transmitter is ~ 2 2,109,618 the same as that at the receiverí- That is, the object is scanned 24 times a second, and each during return deflection thereof in the horizontal and vertical directions. scanning is made along 180 horizontal lines. For the purpose of providing for the automatic During about ninety per cent of each line control referred to above, the signal wave, as period, the picture signals are developed, the am represented in Fig. 2, is supplied by the connec plitude at any instant of the picture current from tion 56 to the grid circuit of a plate circuit de the axis 36 being directly proportional to theI tector 60. 'I'he peak amplitude :t of the syn light intensity at that instant at the correspond chronizing signals is a measure of, or is propor ing elemental area of the object being scanned. tional to the strength of the incoming signals. During the remaining period t of each line This condition is utilized to vary the plate cur period, a synchronizing signal or impulse, indi rent of the tube 60 automatically and substan cated at 38 in Fig. 2, is developed by suitable ap tially proportional to variations in the signal I paratus operating independently of the appara tus for developing the picture signals but syn 15 chronous with it. 'I'he synchronizing signals, therefore, occur at the rate of 4320 a second, and during the periods t, when there are no plc ture signals. 'There are also developed, with the synchronizing signals, other control signals, in 20 dicated at 40 in Fig. 2, where are termed framing ring“ variations in the amplitude :c of the syn chronizing signals. 'I’hat is, the anode end of the resistor becomes more negative with an in-l crease in .'c, and when :c decreases it becomes 20 correspondingly less negative. The electrical potential so developed is applied to the grid cir tially greater duration than the latter. At the transmitter, also, 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 po diate frequency ampliñer 48, as indicated by the larity of the synchronizing and framing signals, The picture signals and the synchronizing and framing signals, transmitted together on a car rier Wave as modulations thereof, are intercepted by an electrical channel A, having at'its input end aradio-frequency, alternating current am plifier 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 40 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 fre 45 quency amplifier 52 supplied from the second detector. y In the output connection 54 from the amplifier 52, the signal wave and the polarities are as rep resented in Fig. 2, with the synchronizing signals in the The ate to tively. “black” direction and of positive polarity. synchronizing and framing signals oper drive the generators 24 and 26, respec The generator 24-begins a new cycle of its operation with the occurrence of each syn chronizing signal. The generator 26, in like man ner, begins a new cycle of its operation upon the occurrence of each framing signal, and this gen erator is so constructed and adjusted that it will not respond to the synchronizing signals which 60 are of substantially shorter duration than the framing signals. The construction and adjustment of the gen erators 24 and 26 is such that they are not af 65 electrical potential is developed whose amplitude 15 varies substantially proportionally with occur signals and occur at the rate of 24 a second. « The framing signals have the same amplitude as the synchronizing signals, but are of substan 30 as indicated in Fig. 2. 50 strength. The result is that across a resistor 59 in the output or plate circuit of the tube 60, an fected 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 con 70 ditions 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 75 sufficiently high to completely cut 01T the ray I6 cuit of one or more of the stages of the interme 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 30 level of the signals applied to the scanning appa ratus I 0 is maintained substantially constant. For the same purpose, the negative control po tential developed in the plate circuit of the tube 60 may be applied to the grid circuit of one or 35 more stages of the radio frequency amplifier 42, as indicated by the broken lines 66. ' For the purpose of normally biasing the grids of the controlled tubes to the best operating po tential, a potential source 61 is provided, the 40 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. By adjusting the bias applied to the grid of the tube 60 from a source 68 the signal amplitude 45 at which the control becomes effective may be determined. In the modification shown in Fig. 4, the pic ture and synchronizing signals are fed directly to the picture signal circuit 58 from the low fre 50 quency amplifier 52, as in Fig. 1. For the pur pose of the automatic control action, however, 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 55 conventional design to pass only the synchroniz ing and framing signals in Fig. 2, rejecting the picture signals of opposite polarity. The ampli iler 10 supplies a suitable form of separating cir cuit 12 which operates to separate the synchro 60 nizing and framing signals, so that in the out put 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, there fore, supplied only with synchronizing signals by the connection 14, andthe generator 26 is sup plied only with framing signals by the connec tion 16. The control signals for the input circuit of the 70 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 75 2,109,618 be correct so that the desired control of sensitivity of the channel A is obtained. In lieu of the tube 80, it will be understood that other known devices, such as a diode or a grid leak rectiñer, can be used for the same purpose, in which case consideration will be given for the correct conditions of polarity of the signals sup plied to the rectiñer device, as will be well under stood. 10 ' From the foregoing, it will be seen that I have provided an improved'television system wherein the receiving apparatus is controlled automatical ly to maintain the level of the picture and con trol signals substantially constant irrespective of 15 occurringr atmospheric disturbances, tuning from one station to another, and the occurrence of any electrical effects which might tend to cause this level to vary, and that for this purpose the syn chronizing signals are used. While but one embodiment of my invention has been disclosed, it will be understood that various modiñcations are possible without departing from 3 said channel comprising an amplifier at the input end thereof, a detector supplied from said am plifler, a second amplifier supplied from said de tector, and a second detector supplied from said second amplifier; a third amplifier supplied from said second detector and operating to supply pic ture and synchronizing signals directly to said ap paratus under conditions such that the picture signals representative of conditions of light at the transmitted subject are of opposite polarity both 10 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 elec trical potential of negative polarity which be comes more negative upon an increase in‘ the ef fective amplitude of the synchronizing signals and which becomes less negative upon a decrease in such amplitude, and connecting means for ap plying such electrical potential to at least one 20 control circuit in said channel effective to vary the sensitivity of the latten» the spirit of my invention or the scope of the 4. In a television receiving system, a cathode ~ ray tube for developing an image of the trans claims. mitted subject and provided with a screen and 25 I claim as my invention: ' 25 1. In a television receiving system, apparatus with means for developing a ray of electrons for developing an image of the transmitted sub and directing the ray at said screen, means for ject, an electrical channel for intercepting pic causing the ray to scan a given area of said screen ture signals and synchronizing signals trans 30 mitted together on a carrier wave as modulations thereof, a rectifier at the output end of said chan nel, an amplifier supplied from said rectifier and operating to supply said apparatus directly with picture signals and synchronizing signals, the 35 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 40 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 elec 45 trical 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. I 2. In the art of television, the method of op 50 eration Which comprises transmitting picture sig nals and synchronizing signals together on a carrier wave as modulations thereof and under conditions such that the picture signals repre sentative of conditions of light at the transmitted subject are of opposite polarity both to the syn 55 chronizing signals and to the picture signals rep resentative of conditions of shade at the trans mitted subject, utilizing the received synchroniz ing signals to develop an electrical potential whose amplitude varies in response to and in ac cordance with occurring variations in the effec tive 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 syn chronizing signals causes an increase in the sen 70 sitivity of said apparatus. 3. In a television receiving system, apparatus for developing an image of the transmitted sub ject, an electrical channel for intercepting picture signals and synchronizing signals transmitted to gether on a carrier wave as modulations thereof; and comprising means for deflecting the ray in a given direction at a given frequency, an elec 30 trical 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 35 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 fre quency, means supplied from said channel with 40 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 re 45 sponse to a decrease in such amplitude, and con necting means for applying such electrical effect to at least one control circuit in said channel ef fective to vary the sensitivity of the latter. 5. In a television receiving system, a cathode 50 ray tube for developing an image of the trans mitted subject and provided with a screen and with means for developing a ray of electrons and directing the ray at said screen, means for caus ing the ray to scan a given area of said screen 55 and comprising means for deñecting the ray in a given direction at a given frequency, an elec trode for Varying the intensity of the ray, an electrical channel for intercepting picture sig nals and control signals transmitted together on 60 a carrier wave as modulations thereof; said chan nel 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 65 amplifier; a third amplifier supplied from said second detector and operating to supply the pic ture and control signals to said electrode under conditions such that the picture signals repre sentative of conditions of light at the transmitted 70 subject are of opposite polarity both to the con trol signals and to the picture signals represen tative of conditions of shade at the transmitted subject, means supplied from said third ampli ñer and operating to develop an electrical eiîect 75 4 2,109,618 - 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 eiîect to at least one control circuit in said channel eiïective to vary the sensitivity of the latter. for maintaining the scanning at the receiver' in synchronism with the scanning at the transmit ter. 7. In a. television system of the type in which picture signals and synchronizing signals are 5. transmitted as a composite signal and in which _ the picture signal voltage representative of con ditions of light is of opposite polarity to the a view is scanned at the transmitter and a screen synchronizing signal voltage with respect to the is scanned at the receiver and in which picture `alternating current axis of said composite sig 10 signals and synchronizing signals are transmitted nal, a receiver comprising a signal channel in 6. In` a television system ofthe type wherein as a composite signal and in which the picture signal voltage representative of conditions of light is of opposite polarity to the synchronizing l 5 signal voltage with respect to the alternating cur rent axis of said composite signal, a receiver comprising an electrical discharge device having a control electrode, means for deriving a uni directional control voltage from` said composite 2 0 signal which voltage varies substantially in ac cordance with the amplitude of said synchro nizing 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 means for utilizing said synchronizing signals cluding an ampliñer for amplifying a carrier modulated by said composite signal and a detec tor located at a later point in said channel for reproducing said composite signal, said ampli 15 iler including a gain control means, means for deriving a uni-directional control voltage from> said reproduced composite signal which voltage varies substantially in accordance with the am plitude of said synchronizing signals as measured 20 from said axis, and means for appplying said control voltage to said gain control means in such direction that the gain of said ampliñer is decreased in response to van increase in the amplitude of said synchronizing signals as meas 25 ured from said axis. ~ ' ` RALPH S. HOLMES.