US2251677A

US2251677A - Television system

Info

Publication number: US2251677A
Application number: US658894A
Authority: US
Inventors: Ralph S Holmes
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1933-02-28
Filing date: 1933-02-28
Publication date: 1941-08-05
Anticipated expiration: 1958-08-05
Also published as: FR768993A; BE401713A; DE767750C; GB434496A

Description

Aug. 5, 1941. R. s. HOLMES TELEVISION SYSTEM I Filed Feb. 28, 1933 4 Sheets-Sheet l ....oom. I lmlm maag.

Aug. 5, 1941. R. s. HOLMES TELEVISION SYSTEM Filed Feb. 28, 1953 Plc Tons l C 4 Sheets-Shea*l 3 SIGN/11:0 r X ENV. 0

P/crums 0 INVEN'T'OR Hal/uh 'S'.Holmea Aug. 5, 1941. R. s. HOLMES TELEVISION SYSTEM Filed Feb. 28, 193s 4 Sheets-Sheet 4 n E 1 l /m n M a 4 1 uw .l H Fw m o m m .1 2 .uw 1 lm s n HM w MPL/PIER I IMPL @1ER Ralph HoZmes (I orneg Patented Aug. 5, 1941 TELEVISION SYSTEM Ralph S. Holmes, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 28, 1933, Serial No. 658,894

(Cl. P18-7.5)

26 Claims.

My invention relates to improvements in television systems.

In one form of television system, an image of the transmitted picture is produced on a iluorescent screen forming part of a cathode ray tube. The tube is provided with a gun for developing a ray of electrons and directing the ray at the screen. If it is desired to reproduce the picture at the rate of twenty frames a second, each frame to have 60 lines horizontally, for example, the cathode ray is deflected horizontally twelve hundred times a second and is simultaneously deflected vertically twenty times a second. Simultaneously with this action, the intensity of the ray is varied in accordance with the received picture signals by applying the latgun and which has a given bias impressed upon It is this bias which controls the average brilliancy or background of the reproduced picture.

In supplying the picture signals to the grid or control circuit of the cathode ray tube, there is an advantage in rst passing the same' through an alternating current amplifier. When this is done, however, the average brilliancy or background intensity of the reproduced picture will be constant, and will, therefore, not correspond ter to a control grid forming part of the electron Y.

to the varying average brilliancy of the picture being scanned at the transmitter. For example,

if a particular picture being scanned has less average brilliancy than the receiver is adjusted to reproduce, as determined by the direct cur-r rent bias on the grid of the receiver tube, the image reproduced on the iluorescent screen will be more brilliant than it should be, and vice versa.

With the foregoing in mind, it is one of the objects of my invention to provide an improved system of the character referred to which embodies an alternating current amplifier supplying picture signals to the control grid of a cathode ray tube, and wherein means are provided for automatically varying the bias on the control grid of the receiver tube in such a manner that the background or total illumination of the reproduced picture at any instant corresponds to and is proportional to the total illumination of the picture being scanned at that instant.

Other objects and advantages will hereinafter appear.

In accordance with my invention, use is made of the fact that synchronizing impulses are transmitted with the picture signals, and are combined with the latter in opposite phase. In passing through the alternating current amplier referred to, the axis of the complete signal wave is at any instant displaced from the so-called zero axis by an amount directly proportional to the average illumination of the picture at the instant, whereby the area under the wave on one side of the instantaneous axis is substantially equal to that under the wave on the other side of this axis. The electrical elfect of this is to cause the peak amplitude of the synchronizing impulses to vary directly with occurring variations of the average illumination of the picture being scanned. This action is utilized in developing a corresponding wave of the correct polarity which, when applied to the control grid of the cathode ray receiver tube, causes the bias to vary in the correct manner so that the background intensity or average illumination of the reproduced picture varies directly with occurring variations in total illumination of the picture being scanned.

My invention resides in the features of construction, arrangement and method of operation of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein Figure 1 is a simplified diagrammatic view of a television receiving system embodying and operating in accordance with my invention;

Figs. 2,3 and 4 are schematic view's illustrative of the operating action in Fig. 1;

Figs. 5, 6 and 'I are views similar to Fig. 1, showing several proposed modilications;

Figs. 8 to 13 inclusive are graphs to which reference will be made in explaining the operation of my improved system; f

Fig. 14 is a diagrammatic view of a television transmitter which may be employed in a television system embodying my invention;

Fig. 15 is a side elevational view of the scanning disc used at the transmitting station looking toward the left in Fig. 14;

Figs. 16 and 17 are enlarged fragmentary views looking toward the left in Fig. 14; and

Figs. 18 and 19 are fragmentary views similar to Fig. 17 illustrating modiiications.

With reference to Fig. l, the numeral I0 designates a suitable form of cathode ray tube provided with a gun l2 for developing a ray I4 ofv electrons and directing the same at a fluorescent screen l 6 on which the transmitted picture is reproduced. Assuming that there are to be 20 frames a second, each frame to have lines horizontally, electromagnetic coils I8 are caused to deflect the ray I4 twelve hundred times a second horizontally, and electromagnetic coils are caused to deflect the ray simultaneously twenty times a second vertically. For this purpose, a suitable generator 22 operates to develop a sawtooth current wave at twelve hundred cycles and to cause this wave to pass through the coils I8, while a suitable generator 24 operates to develop a saw-tooth current wave at twenty cycles and to cause this wave to pass through the coils 20.

Operating action of the receiving apparatus is maintained in synchronism with that at the transmitter by synchronizing impulses eiective to drive the

generators

22 and 24, as will hereinafter more fully appear.

With regard to the various details of construction in Fig. 1, these are assumed to be comparable to those disclosed in more detail in Patent No. 2,137,039, issued Nov. 15, 1938, to Arthur W.

Vance. v

For the purpose of reproducing the transmit-` ted picture on the screen I6, the picture signals are applied to a control grid 26 forming part of the gun l2, whereby the intensity of the ray I4 is made to vary directly proportionally with occurring variations in the picture signals. Adjustment of the rheostat 30 determines the positive potential on the first anode 32.

For the purpose of illustration, it shall be assumed that at the transmitter the object or picture 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 34 are developed, as shown in Fig. 2. Scanning action at the transmitter is the same as that at the receiver. That is, the object is scanned twenty times a second, and each scanning is made along 60 horizontal lines. During about ninety per cent of each line period, the picture signals 34 are developed, the amplitude at any instant of the picture current from the zero axis 36 being directly proportional to the light intensity at that instant at the corresponding elemental area of the object being scanned. During the remaining period t of each line period, a synchronizing impulse 31 is developed by suitable apparatus operating independently of the apparatus for developing the picture signals but synchronous with it. 'Ihe impulses 31, therefore, occur at the rate of twelve hundred a second, and during the periods t, when there are no picture signals. There are also developed, with the synchronizing impulses 31,

framing impulses 38 which occur at the rate of twenty a second.

The impulses 38 have the same amplitude as the impulses 31 but are of substantially greater duration than the latter. At the transmitter, also, the picture signals and the synchronizing and framing impulses are combined in opposite phase, as illustrated in Fig. 4.

At the receiver, the combined wave in Fig. 4 is intercepted and received by a suitable receiver 40 and amplied by an alternating current amplifier comprising the

tubes

42, 44 and 46. By an alternating current amplifier is meant one which has a definite low frequency cut-01T and, therefore, does not pass direct current. The arrangement is such that in the output circuit of the tube 46, to which the grid 2B is connected, the picture signals 34 cause the potential on the grid 26 to become more or less positive with respect to the cathode 28, depending upon the amplitude of these signals, whereas the syn- 'chronizing and framing impulses 31 and 38 drive the bias on the grid 26 negatively to insure that the ray I4 is cut off during return deflectiony thereof in both horizontal and vertical directions.

At any instant, in the alternating current amplifier of which the

tubes

42, 44 and 48 form a part, the instantaneous axis 41 of the picturesignal wave will be \displaced from the zero axis 36 by an amount directly proportional to the average illumination of the picture. The peak amplitude :c of the synchronizing impulses 31 therefore varies directly with the average illumination of the picture being scanned at the transmitter, since these impulses come between scanning line periods during which no picture signals are being transmitted, the picture current then being at a minimum value.

In order to clarify the foregoing, and to explain more clearly the reason why the synchronizing impulses introduced at the transmitter may be utilized, according to my invention, for the purpose of background control at the receiver, attention is first directed to the Bates Patent 1,940,838. 'Ihis patent discloses a television transmitting system wherein, during the interval between scanning lines, when the photocell is not receiving light from the View, synchronizing impulses are introduced by exposing the photocell momentarily to light from a xed source.

By reason ofthe utilization of the same photocell and the picture amplifier in the system of the patent, the synchronizing impulses, obviously, cause the radiated carrier-wave to be periodically modulated to peak values either up or down in the same sense as do very light views, or light portions of a view, being transmitted. Such a signal, at the receiver, may be utilized for background control according to my invention, but it would be necessary to introduce an extra stage of amplification at some point to secure phase reversal of the synchronizing impulses with respect to the picture impulses.

No necessity is seen for illustrating the manner in which the Bates type of signal may be used for background control at the receiver, since I prefer to utilize incoming signals from a television transmitter constructed and arranged according to the disclosure in the Vance patent, referred to. In the said application, means are disclosed whereby the carrier Wave is modulated in one sense by the light portions of the transmitted view and in the opposite sense by the synchronizing impulses. For purposes of convenience, it will be assumed that the dark direction of modulation, corresponding to the synchronizing impulses and dark portions of the view, is up, and that the 1ight" direction is down. That is to say, the carrier amplitude is caused to increasel in response to synchronizing impulses and to decrease in response to light portions of the view. It should be understood, however, that the relative sense of modulation is immaterial since, in my improved receiver the proper utilization of picture and synchronizing impulses depends merely upon the number of stages of amplification and the connections therebetween, it being well known to those skilled in the art that a single resistor-condenser stage provides output potentials that are out of phase with the grid-potentials supplied thereto.

Keeping in mind that at the transmitter the synchronizing impulses are introduced into the system in the dark direction, attention should now be directed to Figs. 8 to 13 of the drawings.

by introducing a dark vcarrier wave.

Figs. 8 and 9 exemplify the transmission of a totally dark view, Figs. 10 and 11 exemplify the transmission of a view that is half light and half dark, and Figs. 12 and 13 are intended to illustrate the transmission of a totally white view. Only five lines from the total number of lines for each view are illustrated, it being obvious that, under the cxtreme conditions I am endeavoring to explain, the time-alternating-current graphs corresponding to the remaining lines of each view will be identicalv with those shown.

Referring first to Figs. 8 and 9, if it is assumed that the all dark View,` Fig. 8, is being repeatedly scanned, the direct current output from the picture photocell at the transmitter will have minimum amplitude and it will continuously correspond, for example, to the line designated Picture which substantially coincides with the zero axis. If the synchronizing impulses are introduced into the picture amplifier, as for example by the use of auxiliary openings in a scanning disc, an auxiliary light source and an auxiliary photocell, as shown in the Vance patent, or by any other suitable means, at line frequency, the said impulses might be graphically represented by the line marked Sync in Fig. 8.

After the synchronizing impulses and the picture impulses are combined in the alternating current ampliers at the transmitter, before being utilized in the modulator, the amplified alternating current output therefrom, with respect to a zero, or reference axis, might be conveniently represented by the line designated Signal in Fig. 9, wherein a: represents the amplitude of the synchronizing impulse with respect to the axis.

Since, as before stated, dark views cause the carrier Wave, preferably, to increase in amplitude, one-half of the carrier wave envelope may be represented by the line entitled Env. in Fig. 9, displaced from the carrier axis a predetermined amount.

The foregoing explanation applies to the additional pair of Figures 10 and 1l, as well as to Figs. 12 and 13, but with the following additional remarks: Between scanning lines there is an interval, as clearly shown in the Vance patent, during which the picture photocell is not exposed to light from the view being transmitted and,

accordingly, its output picture-current is zero. During this interval, the synchronizing impulse is introduced in the so-called dark direction. This condition, I have endeavored to illustrate impulse at the end of each period corresponding to the scanning of a light line and by adding, during the time such impulse is being introduced, the synchronizing impulse in the dark direction. Under these conditions, after passing through the alternating current amplifier at the transmitter, the A. C. axis for the half-white-half-black picture wave in Fig. 11 is further displaced from the tips of the synchronizing impulses than is the case with the all dark picture wave in Fig. 9, and it is still further displaced in the case of the all White picture Wave in Fig. 13. Such being .the case, the amplitudes of the synchronizing impulses, with 'respect to the A. C. axes, are proportional to the the resistor in the output circuit of the tube 46, v

with respect to the alternating current axis, is a measure of the illumination of the view at the transmitter. It is to be noted, however, that the receiving amplifiers have a characteristic that might properly be called electrical memory, and the background change occasioned in the received picture, in the manner hereinafter to be described, is not instantaneously responsive to changes in the view-illumination but is responsive to the average change thereof over a number of picture framea The condition just explained is utilized in the following lmanner to vary the bias on the grid 26 automatically and directly proportionally to variations in the total illumination of the picture or view being scanned. The tube 46 supplies a tube 50 with the wave shown in Fig. 4.

'I'he bias on the grid of the tube 50 is normally zero. On account of the resistor 53 in the grid circuit of this tube, and the fact that the bias on the grid is normally zero, any positive impulses below the instantaneous axis 41 in Fig. 4 operate to impart a positive bias on the grid. It is well known that when the grid of a tube becomes positive with respect to the cathode the grid-to-cathode impedance of the tube decreases.`

Therefore, as the bias on the grid of the tube 50 tends to become more positive, the grid-cathode impedance of the tube 5l) becomes small compared to the impedance of the resistor 53, so that substantially the entire increase in potential appears across the resistor 53, thereby preventing any appreciable change in the plate current of tube 50. The occurrence of a negative impulse above the axis 41 does not have this effect. That is, it does not tend to drive the grid of the tube 50 positive. In such case, on the contrary, the grid-cathode impedance of tube 50 becomes large compared to the impedance of the resistor 53, so

that these negative impulses operate to reduce the plate current of the tube. In this way the current flowing through the plate resistor of the tube 50 is caused to produce impulses whose amplitude varies directionally proportionally with distance :c in Fig. 4. 'I'he impulses 31 and 38 are then applied from the plate circuit of the tube 50 to the grid circuit of the tube 52 by Way of a connection 54. The diode part of this tube recties these impulses and causes variation of the grid, bias in accordance with amplitude variations of the impulses. The plate current of the tube 52 is thereby made to vary directly proportionally to occurring variations in the instantaneous amplitude x in Fig. 4, and by reason of the connection of the grid 26 with the plate circuit of this tube, the bias on this grid is also made to vary in like manner.

The impulses 31 and 38 operate to drive the

generators

22 and 24, respectively. The generator 22 begins a new cycle of its operation with the occurrence of each impulse 31. The generator 24, in like manner, begins a new cycle of its operation upon the occurrence of each impulse 38, and this generator is so constructed and adjusted that it will not respond to the horizontal-synchronizing impulses 31 which are of substantially shorter duration than the framing impulses 38.

In operation, it is understood that as the impulses 31 in the plate circuit of the tube 50 become more positive, the potential at the point 58 becomes correspondingly more negative. 'I'he plate current of the tube 52 and also the potential drop across the resistor 60 thereupon decreases accordingly. In other words, theI potential at the point 62 becomes more positlve, from which it follows that the bias on the grid 26 becomes -less negative with respect to the associated cathode 28. As the impulses 31 become less positive, the reverse action takes place,

' Fig. 6, the tube 46 corresponds to and serves the bias on the grid 26 then becoming more` negative by a corresponding amount. From the foregoing analysis, it will be seen that the control tube 52 operates in the manner set forth to vary the intensity of the ray I4 directly proportionally with variation in the total illumination of the picture being scanned. The average illumination or background of the picture reproduced on the screen I6 is, therefore, made to correspond with conditions of total illumination of the object at the transmitter.

The bias for the control grid 26 is supplied from the plate circuit of the tube 52. This bias is varied by adjustment of the resistors 60 and 6I, and the adjustment is such that for conditions whereat there are no picture signals, the bias is amply suilicient to cut off the ray I4. In other words, when the object transmitted is black, the screen I6 at the receiver tube is dark to correspond.

In the modifications shown in Figs. 5, 6 and 7, the parts corresponding to those in Fig. 1 are designated by the same respective reference numerals as the latter.

In Fig. 5, no extra tube,- such as the tube 52 in Fig. 1, is required. In Fig. 5, however, tube 46 is connected as shown to the output circuit of the tube 42. The amplifier tube 44 is operated With a high bias. Part or all of this bias is supplied by the plate current through a resistor 63. The synchronizing impulses 31 are positive on the grid 64 or this tube, and as they increase in amplitude above the instantaneous axis 41, the plate current of this tube increases and the point 66 becomes more positive. Therefore, on account of the connection 68 to the control grid 26, the bias on the latter becomes more positive with respect to tne associated cathode 28. When the synchronizing impulses 31 decrease in amplitude above the axis 41, the action is just the opposite, the bias on the grid 26 becoming more negative or less positive with respect to the cathode 2B.

The picture impulses are of negative polarity on the grid of the tube 44 and drive the grid beyond cut-olf. Therefore, no current or voltage corresponding to picture signals can appear in the plate circuit of the tube 44.

In Fig. 6, the automatic control action is effected by a grid-bias type rectifier tube 10. This tube is normally biased to a point near cut-off. Therefore, when the positive synchronizing impulses 31 are impressed upon its grid 12, the plate current increases and the potential at the point 14 becomes more negative with respect to ground by an amount directly proportional to the instantaneous amplitude :r of the impulses 31. Since the cathode 28 is always at the same potential as the point 14 on account of the connection 16, as the cathode becomes more negathe same purpose as the tube 46 in Fig. 5.

In 7 the tube 18 corresponds to the tube 18 in Fig. 6. The tube 18, however, is connected and adjusted to operate as a grid-leak rectifier tube,` and operates with no direct current bias. When the positive synchronizing impulses 31 are impressed on the grid 80, the bias increases due to the charge on the condenser 82, thereby causing the plate current to decrease and the potential at the point 84 to become more positive with respect to ground. Therefore, on account of the connection 86 between this point and the grid 26, the bias on the latter becomes more positive with respect to the associated cathode 28, increasing the intensity of the ray I4 accordingly. When the peak amplitude :c of the synchronizing impulses 31 decreases, the action is just the opposite, the intensity of the ray I4 then being caused to decrease directly proportionally.

In the modifications shown in Figs. 5, 6 and 7, it will be understood that the number of stages in the' usual amplifier forming part of the receiver 40 is such that the synchronizing impulses 31 and the framing impulses 38 are of positive polarity in the plate circuit of the tube 4.2, instead of being of negative polarity as in Fig. 1. In Figs. 5, 6 and 7, therefore, these mpulses are of negative polarity in the output circuit of the tube 46 so that they are eiective, as in Fig. 1, to cut off the ray I4 during return deection thereof in both the horizontal and vertical directions.

In the various circuits, the values of voltage, resistance and capacity are adjusted to give the desired control and time constants to meet particular requirements.

From the foregoing, it will be seen that in my improved system the synchronizing or control signals 31 are utilized to automatically effect variation of the average light intensity over the screen I6 in accordance with occurring variations in the average light on the subject being scanned at the instant. In this connection, I believe myself to be the rst to provide a television receiving system wherein an alternating current amplifier is used for the picture signals and wherein the background or average illumination of the reproduced picture is made to vary automatically to correspond with occurring variations in the average light on the subject being scanned at the transmitter, and to accomplish this by utilizing the fact that when the synchronizing impulses are sent through this amplifier with the picture signals, the effective amplitude of these impulses varies directly proportionally vwith occurring variations in average light on the object.

In the practical embodiments of my invention which have been disclosed, satisfactory results have been obtained by using the various types of tubes identified respectively in the trade by the designations given.

For the purpose of more completely illustrating my invention, the transmitter described and claimed in the above mentioned Vance patent is shown in Figs. 14 to 19.

Referring to Fig. 14, a scanning disk is driven by a suitable constant speed motor at 1200 R. P. M., for example, and is interposed in the usual manner between a suitable light source ||2 and a lens or lens system H3. A mask ||4 is supported between the light source and disc H0.

The disc is provided, for example, with sixty scanning holes Ai-Aeo, spirally arranged in the usual manner. The holes Aeu, Ai, and Az are plugged, as indicated. The reason for this will b'e hereinafter explained.

Light reflected from an objectv ||5 excites a photoelectric cell IIS, or a bank of such cells,

to develop picture signals which are amplified by an amplifier and applied to the input line IB of a second amplifier I9. The second amplifier ||9 is connected, as shown, to a suitable modulator |20 which controls a radio transmitter For the purpose of synchronizing operations at the transmitting and receiving stations, electrical synchronizing impulses, at the horizontal synchronizing and framing frequencies, are required. The present improved methods and means for developing these two frequencies will now be explained, with reference more particularly to Figs. to 19.

The disc H0 is provided at the outer edge thereof with concentrically arranged holes ai'to aso, through which light from a light source |22 passes to a photoelectric cell |23, as shown in` Fig. 14. A screen |24, provided with an aperture |25 substantially equal in width to that of the synchronizing holes, is interposed between the disc ||0 and the light source' |22. A Vlens |26 may be employed to focus the light on the photoelectric cell.

There being sixty synchronizing holes, the photoelectric cell |23 develops electrical impulses at a horizontal synchronizing frequency 'of 1200 cycles per second. The impulses or signals at this frequency are amplified by a suitable amplifier |2'| and are supplied directly to the input line ||8 of the amplifier H9, in parallel with the amplified picture signals.

The width of the opening |28 in the mask ||4 is made less than the circumferential distance between adjacent scanning holes, as shown in Fig. 16, to provide for periods during which no picture signals are transmitted. The adjustment of the screen |24 is such that during these periods the synchronizing holes a1 to aso move across the aperture |25.

Three picture lines are omitted by plugging holes Aso, A1, and A2. The synchronizing hole a1 is equal in width to but is longer than the others, and moves across aperture |25 as the plugged hole A1 moves back of the right hand edge of .opening |28.

The above construction and arrangement provides for development, at a vertical edge of the field of view, of impulses at the horizontal synchronizing frequency, and for development, at a horizontal edge of the field of View, of impulses at the framing frequency. The duration of the framing impulses is equal to that of the othersynchronizing impulses because the width of hole a1 is equal to the width of the other synchronizing holes. The amplitude of the framing impulses, however, is substantially greater because of the greater length of hole a1.

From the foregoing, it will be seen that al- When it is desired that the framing impulses f be of greater duration as wellas be greater in amplitude than the other synchronizing impulses, the hole ai in Figs. 15 and 17 is given the shape shown in Fig. 18. That is, vthe size and shape of the framing hole in Fig. 18 is such that the same not only moves across aperture `|25 for a longer period, but during such movement admits more light to the photoelectric cell |23 than the other synchronizing holes.

IfA the requirements are such that the framing impulses be of the same amplitude but of greater duration than the other synchronizing impulses, in order to distinguish the former from the latter at the receiving station, the hole ai in Figs. 15 and 17 is given the shape shown in Fig. 19. That is, the size and shape of the framing hole in Fig. 19 is such that the same moves across aperture |25 for a longer period, and during such movement admits the same maximum amount of light tocell |23 as the other synchronizing holes.

'I'he number of stages in amplifiers ||`|I and |21 is such that the output voltage of amplifier |2'| is 180 degrees -out of phase with that of amplifier ||1, an increase in light intensity on the picture cell 6 causing a corresponding increase, in the positive sense, in the output voltage of amplifier ||1. Therefore, when the synchronizing cell |23 is exposed to the light from source |22, there isa sharp increase, in the negative direction in the output voltage of amplifier |21.

The synchronizing holes a1 to aso may be dis-'- posed on the inside of the scanning'holes, if de- It is also contemplated, if and when s found desirable, to employ a separate disc for sired.

such, and it has been stated that these holes are plugged to omit several picture lines. In actual practice, however, the disc is not apertured at all at these spots.

While the scanning disc has been described as providing for 60 picture lines, it will be understood that the design may be varied to provide for more or less lines, as might be found desirable for particular conditions. Furthermore, the scanning disc may be replaced by a scanning cylinder or other equivalent rotating means of well known construction. If a scanning cylinder is used, the same may be provided with the synchronizing holes, or a separate cylinder may be employed for the synchronizing action, as explained above in connection with the disc construction.

The amplifiers H9, and |20, and the usual power amplifier forming part of the radio transmitter, are of any well known construction having the following desirable characteristics:

(1) Amplification substantially constant at all required frequencies.

(2) The time-lag in the amplifiers to be either zero or substantially constant at all required frequencies.

(3) The amplification to be substantially constant at all required signal amplitudes. The

1. In a television receiving system, an alternating current amplifier for both received picture signals and synchronizing signals, a picture-reproducing device adapted to be supplied with picture signals from said amplifier and comprising screen structure and means for scanning a given area of the latter, means controllable by the synchronizing signals for eiiecting operation of said scanning means to scan said area a.

plurality of times a second, and means for controlling the effectiveness of said scanning means with respect to said screen structure in accordance with a change in the amplitude of the synchronizing signals.

2. In a television receiving system, means for intercepting transmitted picture signals and synchronizing signals, a cathode ray tube provided with a grid for varying the intensity of the ray and operating to produce an image of the transmitted subject, a circuit for supplying the picture signals to said grid, means controlled by the synchronizing signals for eiecting scanning action of the ray, means controlled by the synchronizing signals and operable to develop a wave form representative of occurring variations in the average effective amplitude per frame of the syn- Y chronizing impulses, and a connection between said second-named means and said tube whereby the bias on said grid is caused to vary in accordance with the wave form so developed.

3. In a television receiving system, means for reproducing a transmitted view comprising a cathode ray tube having a fluorescent screen and means for developing a ray of electrons and directing the same at said screen, an electrode forming part of said ray-developing means and effective to control conditions of ray-intensity, means for causing the ray to scan said screen 4comprising a generator of an electrical wave at a definite frequency, and alternating-current ampliiier for received picture signals and control signals in opposite phase to the picture signals" representative of conditions of light at the transmitted view, said generator being supplied with and held in operation at said frequency by said control signals, means supplied from said ampliiler and operating to develop a voltage Wave varying substantially directly proportionally with occurring variations in the eiective amplitude of the control signals in the amplifier channel, and a connection between said last-named means and said tube whereby the voltage wave so developed is eilective to vary the bias on said control electrode in accordance with the shape of said voltage Wave.

4. In the art of television reception, the meth- 0d of operation which comprises developing a cathode ray and directing the same at screen structure, deflecting the ray to cause the same to scan a given area of said structure, intercepting transmitted picture signals and control signals and utilizing the same to control the intensity of the ray and its scanning position on said screen respectively to develop over said area an image of the subject at the transmitter, utilizing the control signals to develop an electrical effect whose amplitude varies substantially proportionally to occurring variations in the average light on said subject, and utilizing the electrical effect so developed to cause a corresponding variation in the intensity of the ray during the scanning of said area.

5. In a television receiving system, means for intercepting transmitted picture signals and control signals, an amplier channel supplied from said means and' operating to amplify both the picture and control signals, a cathode rayl tube for producing an image of the transmitted subject and provided with means for varying the intensity of the ray, a circuit supplied with picture signals from said amplifier channel and connected to said second-named means for eifecting variation in the ray intensity in accordance with the occurring picture-signal variations, means supplied with and controlled by the control signals from said amplier channel and operating to deect the ray, and a second circuit supplied with the control signals from said amplifier channel and operating in the receiving system to develop an electrical eilect which varies in accordance with occurring variations in said system in the effective amplitude of the control signals, and a connection from said second circuit for applying the electrical effect so developed to a point in said system for controlling the same.

6.- In a television receiving system, means for intercepting transmitted picture signals and synchronizing signals, a cathode ray'tube provided with means for varying the intensity of the ray and operating to produce an image of the transmitted subject, a circuit for supplying the picture signals to said second-named means, means controlled by the synchronizing signals for deecting the ray, means controlled by the synchronizing signals and operable to develop a wave form representative of occurring variations in the eiective amplitude of the synchronizing signals, and a connection between said secondnamed means and said fourth-named means.

7. In the art of television, the method of operation which comprises scanning an object to develop picture signals, developing synchronizing signals, transmitting the picture and synchronizing signals together under conditions such that the effective amplitude of the synchronizing signals varies substantially proportionally with occurring variations in the average light intensity over `the scanned area, of the object, scanning screen structure at a receiver to develop an image of the object, utilizing at the receiver the synchronizing signals to control the scanning position on said screen structure, utiliz- 'ing at the receiver the synchronizing signals to develop a wave representative of occurring variations in the eiective amplitude of the synchronizing signals, and utilizing the wave so developed to vary conditions of average light intensity over said image in a manner corresponding to occurring variations in average light in- -tensity over the area of the scanned object at the transmitter.

8. A television receiver for the reception of a composite signal including picture signals and synchronizing signals, the picture signal voltage representive of conditions of light being of opposite polarity to the synchronizing signal voltage with respect to the alternating current axis of the composite signal and the synchronizing signals varying in amplitude in accordance with the average illumination of a view being transmitted, said receiver comprising means for reproducing a picture, said means including means for producing a scanning ray, means for causing said ray to scan a certain area, and also including a control circuit; for modulating said ray, means for utilizing said synchronizing signals for controlling the scanning position of said ray on said area, means for supplying the picture signals to said control circuit, means for deriving a unidirectional control voltage from the said received synchronizing signals of changing amplitude which varies in response to a change in said average illumination, and means for applying said control voltage to said control circuit.

9. A television receiver for the reception of a composite signal including picture signals and periodically recurring synchronizing signals, the synchronizing signal voltage being of greater amplitude than the picture signal voltage and varying in amplitude with respect to the alternating current axis of the composite signal in accordance with the average illumination of a view being transmitted, said receiver comprising a cathode ray tube having a control electrode, means for causing the cathode ray of said tube to scan a certain area, means for utilizing said synchronizing signals to control the scanning position of said ray on said area, means for impressing the received picture signals upon said control electrode and for deriving from said received synchronizing signals of changing amplitude a unidirectional potential which changes in -response to a change in said average illumination, and means for applying said uni-directional potential to said control electrode as a bias.

10. A television receiver for the reception of a composite signal including picture signals and synchronizing signals, the picture signal voltage representative of conditions of light being of opposite polarity to the synchronizing signal voltage with respect to the alternating current axis of the composite signal, said receiver comprising a cathode ray tube having a fluorescent screen, means for causing the cathode ray of said tube to scan said screen, means for utilizing said synchronizing signals to control the scanning position of said ray on said screen, means for deriving a uni-directional control voltage from the received synchronizing signals which varies in response to a change in the average illumination of the view being transmitted, and means for so controlling the cathode ray in said tube in accordance with said control voltage and the received picture signals that a picture is formed on said screen as it is scanned by the cathode ray which has an average illumination of said view.

11. A television receiver for the reception of a composite signal including picture signals and 'synchronizing signals, the synchronizing signal voltage being of greater amplitude with respect to the alternating current axis of the composite signal than the picture signal of the same polarity as said synchronizing voltage, said receiver comprising a cathode ray tube having a iluorescent screen, means for scanning said screen by the cathode ray under the control of said synchronizing signals, means for deriving a uni-directional control voltage from the received synchronizing voltage which varies in response to a change in the average illumination of the view being transmitted, and means for so controlling the cathode ray in said tube in accordance with said control voltage and the received picture signals that a picture is formed on said screen as it is scanned by the cathode ray which has an average illumination corresponding to the average illumination of said view.

12. In the art of television reception wherein a composite signal comprising picture and synchronizing signals is applied to the grid circuit of a cathode ray tube to eiect reproduction of a view, the method of operation which comprises applying said picture signals directly to said circuit, causing said cathode ray to scan a certain area, controlling the scanning position of said say/by said synchronizing signals, deriving from the received synchronizing signals a uni-directional potential, and introducing said potential into said circuit.

13. A television receiver for operation in a system in which picture signals and synchronizing signals are transmitted as a composite signal and in which the direct current component of the picture signals is lost during transmission, said receiver comprising a cathode ray tube having a fluorescent screen, means for scanning said screen by the cathode ray under the control of said synchronizing signals, means flor modulating the cathode ray in accordance with saidpicture signals and means for deriving from said received synchronizing signals a control signal corresponding to said lost component and inserting said control signal in said modulating means.

14. The method of reception of a composite signal comprising picture signals and synchronizing signals` in which signal the low frequency components representative of the average illumination of a view being transmitted are lost, which method comprises causing a ray to scan a certain area, modulating said ray by said picture signals, controlling the scanning position of said ray by said synchronizing signals whereby there is reproduced a picture in accordance with said.

composite signal, deriving from the received synchronizing signals a control signal which represents said low frequency components, and varying the average illumination of said reproduced picture in response to variations in said control signal.

15. In a television system of the type in which a carrier wave is modulated by picture signals and by synchronizing impulses, and in which said impulse modulation is introduced into the carrier in the same-direction as the modulation thereof by dark portions of va view being transmitted, a receiver including a cathode-ray tube having a control electrode and a deflecting device and a saw-tooth wave generator coupled thereto, a vacuum tube having input electrodes and an output circuit, means for impressing said signals and impulses upon said input electrodes, means for rendering said vacuum tube effective to transfer said synchronizing impulses and substantially ineiective to transfer said picture signals, means for impressing at least part of the synchronizing impulses appearing in said output circuit upon said generator, and means for applying a biasing voltage to said control electrode which varies slowly in response to a change in the amplitude of said synchronizing impulses.

16. In a television system of the type in which picture signals and both horizontal and Vertical synchronizing signals are transmitted and in which at least the greater part of the picture signal voltage is of opposite polarity to the synchronizing signal voltage with respect to a given axis, said vertical synchronizing signals occurring at a lower frequency than said horizontal synchronizing signals, a receiver comprising a cathode-ray tube having a control electrode, a horizontal deflecting device, and a vertical deiiecting device, a saw-tooth wave generator coupled to said rst device, a saw-tooth wave generator coupled to said second device, an electric discharge tube having input electrodes and an output circuit, means for coupling said output circuit to said generators, means for impressing said picture signals and said synchronizing signals upon said input electrodes, means for rendering said tube effective to transfer said synchronizing signals and substantially ineffective to transfer said picture signals, and means for applying a biasing voltage to said control electrode which varies slowly as compared with the frequency at which said vertical synchronizing signals occur in response to a change in the amplitude of said synchronizing signals.

17. In a television system of the type in which picture signals and synchronizing signals are transmitted as a composite signal, a receiver comprising a cathode ray tube having a control electrode, means for causing the cathode ray in said tube to scan a predetermined area, means for utilizing said synchronizing signals to control the scanning position of said cathode ray on said area, means for deriving a uni-directional control voltage from said composite signal which voltage varies substantially in accordance with the amplitude of said synchronizing signals as measured from the alternating current axis of said composite signal, and means for applying said control voltage to said control electrode whereby the intensity of said cathode ray varies in accordance with said amplitude.

18. In a television system of the type in which picture signals and synchronizing impulses are transmitted as a composite signal with said impulses of greater amplitude than said picture signals, a television receiver which includes a cathode ray tube having a fluorescent screen, a cath- 4ode ray deflecting device and a control electrode,

means controlled by said synchronizing impulses for applying a deflecting wave to said device in synchronism with the occurrence of said impulses, and means for applying a biasing potential to said electrode which varies in response to changes in the height of said impulses with respect to the alternating current axis of said composite signal for controlling the average illumination of a picture formed on said screen.

19. In a television system of the type in which picture signals and synchronizing signals are transmitted as a composite signal with the synchronizing signals of the same polarity as picture signals representative of black and of a greater amplitude than picture signals representative of black, a cathode ray tube having a uorescent screen, deilecting devices and a control electrode, means for applying deflecting waves to said deflecting devices for scanning said screen and for synchronizing said waves with said synchronizing impulses, means for impressing said picture signals upon said control electrode Aand for deriving a uni-directional biasing voltage from said synchronizing impulses which varies in value in response to a change in the peak amplitude of said synchronizing signals, and means for so applying said biasing voltage to said control electrode that the intensity of the cathode ray increases in response to an increase in the amplitude of said synchronizing signals.

20. In a television system wherein a composite signal comprising picture signals and synchronizing signals is developed and in which the direct current component of the picture signals is lost during transmission through an alternating current amplier, an electric discharge tube in said system following said amplifier and having a plurality of electrodes, means for deriving from said synchronizing signals a control signal corresponding to said lostl component, and means for applying said lost component to one of said electrodes, and means for controlling the deflection of a cathode ray in accordance with said synchronizing signals. e

21. In the art of television reception wherein incoming signals are received, the method of operation which comprises scanning a given area of screen structure with an agent a plurality of times a second to produce an image of the transmitted subject, utilizing said incoming signals to control the position of said agent on said screen, and utilizing said control signals during the scanning a'ction to control the influence of the scanning 4agent with respect to said screen structure to determine the degree of average light intensity over the image.

22. The method of transmitting and receivin'g pictures which comprises transmitting a composite signal consisting of picture signals and synchronizing impulses, intercepting said composite signal at a receiver, converting said picture signals into a light image of the subject being transmitted, utilizing said synchronizing impulses for maintaining synchronism between the transmission and conversion of said picture signals, and utilizing said synchronizing impulses also for automatically maintaining the average illumination of said light image substantially the same as the average illumination of the subject being transmitted.

23. The method of transmitting and receiving pictures which comprises transmitting a composite signal consisting of picture signals and synchronizing impulses, intercepting said composite signal at a receiver, converting said picture signals into a light image of the subject being transmitted, synchronizing the conversion of the picture with the transmitter by the impulses and maintaining the average illumination of the converted image substantially the same as the average illumination of the subject being transmitted in accordance with the impulses serving to synchronize the conversion.

24. The method of transmitting and receiving pictures which comprises transmitting picture signals and synchronizing energy, intercepting said picture signals and synchronizing energy at a receiver, converting said picture signals into a light image of the subject being transmitted, synchronizing the conversion of the picture with the transmitter by the synchronizing energy and maintaining the average illumination of the con- 4 verted image substantially the same as the average illumination of the subject being transmitted in accordance with the synchronizing energy serving to synchronize the conversion.

25. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting areceived wave to derive therefrom the modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene, a peak voltage rectifier for rectifying the synchronizing frequency components of the modulation voltages to derive therefrom a unidirectional voltage, and means for utilizing said undirectional voltage for controlling the average intensity of said beam.

26. A television receiving system for carrier Waves of the type having modulation including Video-frequency and line-frequency-synchronizing and picture-frequency-synchronizing cornponents, comprising means for selecting, amplifying and detecting a received Wave to derive therefrom the modulation voltages,v a screen, a source of a scanning beam for said screen, means controlled by said synchronizing-frequency components of the modulation voltages for effecting Cil scanning of said screen by said beam, means responsive to the Video-frequency components of said modulation voltages for effecting variation in the intensity of said beam to reproduce a scene, a peak voltage rectifier, means for supplying said line-frefluency-synchronizing components to said rectier to develop a unidirectional voltage of anv amplitude substantially equal to the amplitude of said 'line-frequency-synchronizing components, and means for utilizing said uni-directional Voltage for controlling the average intensity of said beam.

RALPH S. HOLMES.