US2192121A

US2192121A - Television system and the method of operation thereof

Info

Publication number: US2192121A
Application number: US728147A
Authority: US
Inventors: Alda V Bedford
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1934-05-29
Filing date: 1934-05-29
Publication date: 1940-02-27
Anticipated expiration: 1957-02-27
Also published as: GB448065A; BE409634A; NL44375C; BE434568A; BE414088A; DE714155C; FR790492A; BE414635A; DE716028C; DE685918C; BE424847A

Description

Feb. 27, 1940.

A. v. BEDFORD TELEVISION SYSTEM AND THE METHOD 0F OPERATION THEREOF Original Filed May 29, 1954 5 Sheets-Sheet 1 www A. V. BEDFORD Fen 27, 1940.

TELEVISION SYSTEM AND THE METHOD 0F OPERATION THEREOF O rignal Filed May 29, 1954 5 Sheets-Sheet 2 IN1/Mme:

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TELEVISION SYSTEM AND. THE METHOD 0F OPERATION THEREF Original Filed May 29. 1934 5 Sheets-Sheet 5 y WTTOE/VE 5 Sheets-Sheet 4 Feb. 27, 1940. A. v. BEDFORD TELEVISION SYSTEM AND THE METHOD oF OPERATION THEREOF Original Filed May `29, 1934.

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A, v. BEDFORD TLEVISION SYSTEH AND THE METHOD 0Fv QPERATION THEREOF original Filed- May 29, 1954 5 sheets-sheet 5 Iig/31.

PHO/0 P505/VER Patented Feb. 27, 1940 TELvISIGN SYSTEM AND THE METHOD 0F OPERATION THEREOF l Aldo v. Bedford, Collingswood, N. J., mignonto Radio Corporation of America,

Delaware a corporation of Apoiiootion Moy 29, 1934, serial No. 723,147

My invention relates to improvements in television systns and the method of operation thereof.

In television systems embodying a cathode ray 5 tubeV at both the transmitting .and receiving stations, Vit has been found to be advantageous to cause the cathode rays to scan the respective screens in such manner that the horizontal lines of alternate frames fall in 'the spaces between the horizontal lines `of the intervening frames. For example, the 'horizontal lines of the odd frames are spaced a distance about equal to the width of a line, and the Vhorizontal lines of the even frames, which are similarly spaced, fall between the lines of the odd frames. On account of the persistency of visionthe optical effect is the same as though each frame comprised twiceA the number of lines. A- system of this type is disclosed in the copending application of Ran-y dall C. Ballard, Serial No. 623,325, filed July 19, 1932. This distinctive action of scanning is sometimes referred to as interlaced scanning. For the purpose of obtaining the socalled interlaced pattern, the cathoderay.v is deflected horizontally an odd number of times every two frames, the relation of the line frequency to the frame frequency being such that the scanning of each odd framey starts at the same point at the upper left hand corner of the screen, while the scanning action for each, even frame starts at the same point which is a distance of one-half a line to the right from the common starting point for the rodd frames. In this way, the lines of the even frames are disposed in the spaces between the lines of the odd frames.

For the purpose of synchronization and framing in the systems referred to, a synchronizing signal is transmitted at the end of each scanning line and utilized at the receiver to drive the circuit for defiecting the cathode ray horizontally. At the end of each frame a framing signal is transmitted and utilized at the receiver to drive the circuit for deiiecting the ray vertically. On account of the relation referred to, the odd and even framing signals occur at different times with a respect to the synchronizing signals. The eifect of this, at the receiver where a filter is used to separate the synchronizing signals from the framing signals, is to cause the odd framing signais to have `a slightly different shape than the even framing signals in ,the output connections from the iilter. The precise timing required to obtain the uniform spacing, of the interlaced lines is therefore lost unless the various adjustments and operating conditions are exactly right.

Renewed June 17, 1938 In the systems referred to, furthermore, occurrence ofthe framing signals prevents any synchronizing signals from being eective during the periods of occurrence of the framing signals. During these periods, therefore, a relatively slight electrical disturbance or misadjustment is effective to cause the scanning action at the receiver to fall out of time with that at the transmitter.

In the systems referred to, furthermore, undesirable electrical effects are developed due to return deflection of the cathode ray at the transmitter, the action of cutting oi the ray during the return line periods, and, in the transmission of moving picture film, the action of iiashing images of the pictures onto the photos'ensitive surface of the usual screen.

In the various television systems proposed heretofore, furthermore, the direct current component of the signals is lost during the operating action at the transmitter. The effect of this is manifested at the receiver by production of an image whose overall brilliancy or background does not necessarily correspond with that of the object being transmitted.

With the foregoing in mind, it is one of the objects of my invention to provide an improved television system and method of operation whereby the odd and even framing signals referred to above are, for all practical purposes, identical at the points or connections whereat they are used to control the vertical deiiecting circuit, so that deflection of the cathode rays is more readily and accurately controlled than has been possible by the various systems and methods proposed heretofore.

Another object of my invention is to provide an improved television system and method of operation in which the undesirable electrical signals or other disturbing electrical effects referred to are either eliminated or compensated for at the y transmitter without interfering with the development and transmission of the desired picture, synchronizing and framing signals. f

Another object of my invention is to provide an improved television system yand method of operation whereby there is developed a signal wave which forms part of and is transmitted with the entire signal wave. 'Ihis signal Wave is representative of the required. direct current component which can be utilized at the receiver to vary the background of the reproduced picture automatically and in accordance with occurring variations of the overall brilliancy or background of the `object at the transmitter.

' with a screen I2.

framing signals are interrupted, and synchronizing signals are caused to occur during the interruption periods whereby the circuit for horizontal deection of the ray is supplied with synchronizing signals during the framing periods.

The action is s "l1 that interruption of the frami ing signals does not interfere with their effectiveness in controlling the circuit for vertical deflection of the cathode ray. Y

Further, in accordance with my invention, the picture signals developed at the transmitter are supplied to an ampliier comprising a plurality of tubes, some of which are driven to saturation during the periods of return deection of the ray so that the undesirable electrical signals developed during these periods do not appear in the output wave from the amplier. At a later stage in the ampliiier, the synchronizing and framing signals aresupplied and transmitted with the picture signals.

My invention resides in the improved system 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 draw-` ings, wherein Figure 1 is a diagrammatic view of a television transmitting system constructed and operating in accordance with my invention;

Fig. 2 is an enlarged, detail, sectional view,

the section being taken on the line 2-2 in Fig. 1;

Fig. 3 is an enlarged elevational view of the disc in Fig. 1 for developing the synchronizing and framing signals;

Fig. 4 is an enlarged fragmentary view, taken from Fig. 3;

5 to 20 are graphical views, illustrative of the principle of operation in Fig. l;

Fig. 21 is a diagrammatic view of one form of television receiving apparatus for intercepting and utilizing the signals transmitted by the systernl in Fig. 1 to produce an image of the object; and

the circuits in Fig. 1.

With reference to Fig. 1, the picture signals are developed by a cathode ray tube I 0 provided- This screen is of the usual construction and comprises a sheet of insulation j.

material provided on the surface I4 thereof with a large number of minute, metallic, photosensitized elements, spaced and insulated from each other. The insulating sheet is provided over the opposite 'surface thereof with a sheet or coating of electrically conductive material to which an output connection I6 is made.

The tube I0 is provided with an electron gun I8 for developing a ray 20 of electrons and diresting the same at the mosaic photosensitive surface I4 of the screen. The gun comprises a cathode 22, a grid 24 for controlling the intensity of the ray, and an anode 2S-for accelerating the Fig. 22 is a detail diagrammatic view'of one of l electrons. A second anode 28, which may be in the form of a lsilver coating on the inside surface of the tube, is maintained at a relatively high potential positive with respect to the potential on the nrst anode 26, and operates in cooperation with the latter to focus the ray of electrons to a relatively small spot on the screen I2. The various electrodes of the tube are supplied as usual with suitable operating potentials, as represented in the drawings.

For the purpose of causing the ray 26 to scan the screen I2, a circuit 36, connected as shown to the coils 3.2, develops a voltage wave of the required shape and frequency to cause a sawtooth current Wave to pass through .these coils at a frequency of 7290 cycles, and a circuit 34,'connected as shown to the coils 36, develops a voltage wave o1' the required shape and frequency to cause a saw-tooth current wave tov pass through the coils 36 at a frequency of'60 cycles. Under these conditions, during every odd frame the ray is made to scan the screenl along the same horizontal lines spaced from each other a distance about equal to the width of a line, and during every even frame to scan the screen along the same horizontal lines which always fall in l the spaces between thelines of the odd frames.

The object is represented as being a moving picture nlm 38, and the apparatus for projecting the individual pictures onto the screen surface I4 is shown as being the same as that descn'bed in detail in my copending application, Serial No. 653,947, filed January 28, 1933. This apparatus comprises a disc 40 provided with diametrically opposite openings 42 and 44 and driven at a constant rate of revolutions a second by a synchronous motor 46. The lm 38 is fed intermittently through a gate 48 atthe rate of 24 pictures a second by means of suitable intermittent during the periods that theopenings 42 andA 44 expose the screen I2 to the light, and these periods are equal to and occur simultaneously with the periods during which return deflection of the ray 20 takes place in the vertical direction. During the periods that the disc III cuts off the light to the screen I 2, the ray 20 scans the screen once.

'I'he action of the intermittent mechanism 50 is such that each of the odd pictures, for example, is left stationary in the iilm gate 48 for projection three times onto the screen I2, while each of the even pictures is held stationary in the film' gate for projection twice onto the screen. Since 12 odd pictures and 12 even pictures are fed through the gate 48 every second, there will be periods every second during which an image of a iilm picture isflashed onto the screen I2. Due to this action, it is possible to feed the lm at the rate of 24 frames a second and to scan the screen I2 at the rate of 60 times a second.

The means for developing the synchronizing and framing signals comprises a disc 54 which is rotated at the rate of 30 revolutions per sec.- ond by a synchronous motor 56 supplied from the same source 58 as the motor 46.

Light from a source 88 is focused on this disc, and passes through openings therein disposed and shaped as shown in Figs. 3 and 4. A photoelectric cell 62 exposed to the light coming through these openings develops the synchronizing and framing signals. These signals are amplified by an amplifier 64 and supplied to a filter 85 which separates the two kinds of signals. The synchronizing signals are taken from the filter by a connection 66 and supplied to the horizontal.

deflection circuit 38. A connection 88 from the filter supplies the framing signals to the vertical deflection circuit 3,4.

For the purpose of causing the maximum of light to reach the photoelectric cell 62, the lens 18 is used to focus the light from a source 68 on a slit 12 in a mask 14, and a second lens 16 is used to focus the light from the slit 12 on the openings in the disc 54, as more clearly shown in Fig. 2. The openings in the disc 54 through which light from the source 68 shines are in the form of slits 18, 243 in number, evenly spaced, and disposed at the outer edge of the disc. The slit 12 is about the same size and shape as the slits 18.

'Ihe disc 54 is also provided with two

openings

88 and 82 diametrically opposite to each other, and through which the light shines to develop the framing signals. As shown in Fig. 4, the framing opening 88 is interrupted tovmake room for a synchronizing slit 18, and the framing opening 82 is likewise interrupted to make room for a synchronizing slit 18. The areas of the sectional openings comprising the

openings

88 and 82 are such that the total open area in each case is equal, so that the same amount of light will pass through each of these openings. Additional slits 84, similar to and spaced the same as the slits 18, are disposed as shown about the framing opening 88 and between the slits 18. One of the slits 84 is disposed in the remaining gap in the framing opening, as shown. Likewise, additional slits 86, also similar to and spaced the same as the slits 18, are disposed about the framing opening 82. One of the slits 86 is disposed, as shown, in the remaining gap in the openings 82. With the disc 54 rotating at the rate of 30 revolutions a second, synchronizing signals will be developed at the rate of 7290 a second, and framing signals will be developed at the rate of 60 a second. These signals are applied by a connection 88 and through a resistance 98 to the output connection 82 from an amplifier comprising the tubes 94, 96, 88, |88 and The disc 54 is also provided with a second set oi' slits |84 evenly spaced about the edge of the disc by an amount to make room for 243 of these openings. Elongated openings |86 and |88 are disposed diametrically opposite and on the same circumference as the slits |84. Each of the openings |86 and |88 extends over a distance equal to about seven times the distance between two adjacent slits |84. The effect of this is to develop a relatively strong signal of substantially constant amplitude and which occurs during the period of each return deflection of the ray 28 in the vertical direction. -Light from a source ||8 shines through the slits |84 and the openings |86 and |88'to a photoelectric cell ||2 to develop electrical signals which are amplified by an amplifier ||4. The disposition of the slits |84 is such that a signal is developed at the end of each scanning-line period. The purpose of these signals will hereinafter more fully appear. Light from the source ||8 is focused on the slits and openings in the same manner shown in Fig. 2.

` The amplied signals from the amplifier 4 are applied by way of a condenser ||6 and a connection ||8 to the control grid 24 of the electron gun, and are taken from a stage of this amplifier whereat they are of negative polarity and of sufficient amplitude to cut the ray 28 off during each of the periods of return deflection of the ray in both the horizontal and vertical directions. The signals from the amplifier ||4, at positive polarity, are also applied by Way of a resistance |28 and a connection |22 to the grid circuit of the tube 96.

'I'he disc 54 is also provided with openings |24 and |26 disposed diametrically opposite to each other and concentrically about the axis of rotation. The length of each of these openings is about twelve times the distance between two adjacent slits |84. Light from a source |28 is focused on the openings |24 and |26 in the same manner shown in Fig. 2, and excites a photoelectric cell |38 to develop relatively strong signals each of a duration equal to twelve times a scanning-line period. These signals are amplified by an amplifier |32 and, at positive p0- larity, are applied by way of a resistance |34 and connections |36 and |22 to the grid circuit of the tube 96.

'I'he picture signals developed by the tube |8 are amplified by an amplifier |31 and applied by a connection |38 to the grid circuit of the tube 84.

With 243 synchronizing signals occurring for every two framing signals, for the purpose of obtaining the so-called interlaced scanning action, as explained, the framing signal for every odd frame, represented at 88:1: in Fig. 5, and the framing signal for every even frame, represented at 82:1:v in Fig. 6, would occur at different times with respect to the synchronizing signals represented at 18x. The effect of this, in the systems proposed heretofore, is illustrated in Fig. 7. The full line curve4 |35 represents what the output wave in the line 68 from the filter 65 would' be for the even frames, and the broken line curve |31 represents what the output wave in the line 68 would be for the even frames. Due to the retention in the filter 65 of the charges produced b'y the synchronizing signals in the input wave to the filter, the curves |35 and |31 will differ in size and shape, as represented. The framing signal for each odd frame, represented at 88g, and the framing signal for each even frame, represented at 82g, will therefore be different in size and shape. For this reason, the timing for vertical deflection of the cathode ray tends to be inaccurate, in which case the odd and even lines will not `have the required spacingand positions with respect to each other to obtain a properly interlaced pattern.

As explained, another disadvantage of the conditions as represented in Figs. 5, 6 and '7 resides in the fact that occurrence of each framing signal prevents any simultaneously occurring synoccur auxiliarysignals as represented in Fig. 8

at 84a, and these signals willrbe similar to the synchronizing signalsand will occur at the same times as the synchronizing signals would occur if the frequency of the latter were doubled during aperiod of time slightly greater thanand embracing the period of occurrence of the framing signal represented at 80a. As represented in Fig. 8, one of. the auxiliary signals occurs during a period of interruption of the framing signal represented at 80a. In like manner, due to the additional slits 86 in Fig. 4 there will occur auxiliary signals represented at 86a in Fig. 9,'

similar in size and shape to the synchronizing signals. One of these auxiliary signals occurs during a period of interruption of the framing signal for the even frames, as shown. These auxiliary signals will occur at the same times as the synchronizing signals would occur if the frequency of the latter were doubled during a period of. time slightly greater than and embracing the period of occurrence of theframing signal for the even frames, represented at 80h. h

'I'he synchronizing and framing signals or impulses shown in Figs. 8 and 9 may be described from a somewhat different viewpoint. To assist in the description, the several portions of the framing signal 80a which are separated by the interruptions are indicated as 80m, 80a2 and 84aa While the several portions of the framing signal 80h are indicated as 88171, 80172 and 80173.

The space between the signal portions 80a1 and 84a may be referred to as a slot. The space between portions 80a2 and 18a is another slot. Likewise, the space between 80171 and 18h and the space between 801m and 86a may be referred to as slots in the framing signal.

Thus, the back or trailing edge of the slot between 80m and 84a occurs in the same time relation as the front or leading edges of` the horizontal synchronizing signals. The same is true of the slot between 80a2 and 18a with respect tothe auxiliary signals. The same thing, of

course, is true of the slots in the framing signal It will be noted that the back edges ofthe above-mentioned slots in the framing signals increase in amplitude in the same direction with respect to time, as do the front or leading edges of the horizontal synchronizing signals andthe auxiliary signals. Therefore, these back edges produce the same kind of signal in the horizontal separating or diierentiating circuit yshown in Fig. 2,1 as do the front edges of the horizontal synchronizing signals.

The signal shown in Fig. 8 may also be described accurately by saying that the framing signal portions 80:11, 88a2 and 80:13 follow,` or occur immediately after, the synchronizing

signals

18x, 84a and 18a, respectively.

With conditions as represented in Figs. 8 and 9, there is greater symmetry of the synchronizing signals with respect to-the framing signals for the even and odd frames. The result is that the output wave from the filter 65 for the odd frames will be as represented in Fig. 10 by the curve 802:, and the output curve from this amplier for the even frames will be as represented by the brokenune curve sie. with the electrical waves for vboth the oddand even frames practically'identical during the periods Aoi occurrence` ftheiraming signals, the latter will be the'same, i 'gsize and shape for bothv the odd'and even frames ,For this reason thev timing for'vertical deiiection of vthe raywill be'accurate, so that the vrespective points at which the ray Lstarts to scanJthe'odd and evenl frames kwill be .definitely fixed to maintain the desired action for interlaced scanning,

evenv though there might occur a relatively slight electrical disturbance or misadjustment. `While the additional or auxiliary'signals represented at 84a and 86a are similar to the synchronizing signals, they are not effective to change the frequency of operation of the horizontal .deilecting circuit 30 for the reason that this circuit has considerable inertia" which makes it insensitive to any signals except those which are occurring in time with its natural period of oscillation. f

even framing signals are made substantially the same in size and shape, might be improved further by making some of the slits 84 andA 86 slightly wider or narrower than the others, or by making one or more of. these slits wider and one or more of these slits narrower than the others.

The eiect of this is to cause the duration of one or more of the auxiliary signals to be less than that of the others, as represented by dash lines in Fig. 8, or the duration of one or more of the auxiliary signals to be greater than that of the others, as represented by `clash lines in Fig. 9. Another modification of wave shape which would produce substantially the same result is one inv which the

additional impulses

84a and 86a are omitted and the vertical synchronizing impulses 80a`and 80h are made slightly different from one another in shape or duration in order to compensate the dissymmetry of timing of the horizontal synchronizing impulses 18x with respect to the vertical synchronizing impulses.

The synchronizing signals which occur during the periodsof. interruption of the framing signals are eiective to drive the horizontal deilection circuit 30. This circuit is therefore positively driven at all times, so that it does not drift out of synchronism during the interval of the framing signal.

It has been determined that although the framing signals are interrupted for the purpose explained, they are still effective'to drive or control the vertical deflection circuit 34 satisfactorily.

The filter 65 permits substantially only the synchronizing signals to pass to the horizontal deiiection circuit 30 by way of the connection 66, and only substantially the framing signals, which have a substantially diierent steepness of wave front than the synchronizing signals, to pass to the vertical deflection circuit 34 by way of they been exposed.` As the ray 20 is deiiected horizontally across the screen from left to right, as

viewed looking toward the right in Fig. 1, picture signals represented at |42 in Fig. 11 are developed during the time T in the output connectionl |38 The action just described, whereby the odd andv from the amplifier |31. vAt the endof this time. a synchronizing signal occurs and is effective with respect to the horizontal deilection circuit 30 to cause return deflection of the ray during the time t. During the time t. one of the signals from the amplifier ||4, represented at |44 in Fig. 13, is applied at negative polarity to the grid 24 to cut of! the ray 20. One of these signals occurs during each of the return periods t. The action of cutting of! the ray andvdeilecting it back aero@ the screen causes development, during the periods t, of undesirable signals represented at |48 in Fig. 11.

At the end of each'frame a framing signal occurs and is eiective with respect to the vertical deflection circuit 34 to cause return deection of the ray in the vertical direction, this action taking place during a period equal to 4(T+t).

At this time a signal, represented at |48 in Fig. 18, and which is caused by one of the openings |06 and |08 in Fig. 3, occurs, and is applied at negative polarity to the grid 24 to cut off the ray. The action of cutting off the ray at this time and causing it to return vertically produces an undesirable signal.

The action of ilashing the pictures onto the screen |2 in the manner explained occupies a period equal to 12(T+t) and causes development in the output connection |38 of an undesirable signal represented at |50 in Fig. 11. During this same period, one 4of the openings |24 and |26 is effective to cause development in the connection |36 of an electrical signal represented at |52 in Fig. 14, and which is of positive polarity.

With the arrangement and connections as described and shown in Fig. 1, the electrical wave in the output connection |38 from picture-signal amplifier |31 will be as represented in Fig. 11, with the picture signals representative of conditions of light at the object, of positive polarity. This wave is applied to the grid circuit of the tube 94, as shown. In the output circuit of the tube 94 this wave will be the same shape as that in the grid circuit, but will be reversed in polarity, as represented in Fig. 12.

The wave from the output of the amplifier |4, and in the resistance |20, will be as reprtfented in Fig. 13, with the signals of positive p larity. The wave from the output of the amplifier |32, and in the connection |36, will be as represented in Fig. 14, with each signal of positive polarity. The waves yas represented in Figs. 13 and 14 are applied by the connection A|22 to the grid circuit of the tube 86 and combine With the wave of Fig. 12 to produce an input wave to the tube 96 as represented in Fig. 15. This wave is reversed in polarity by the tube 96, and appears in the plate circuit thereof as represented in Fig. 16. 'I'he wave as represented in. Fig. 16 is applied to the input circuit of the tube 98 which is so biased that any signals. more negative than those at the level represented at |60 in Fig. 16, are effective todrive this tube to Vcut oiT. In this way practically all the undesirable signals which were developed during the periods of horizontal and vertical return deflection of the ray are eliminated. The output wave from the tube 98 will therefore be as represented in Fig. 17, and will be reversed in polarity by the tube |00 and appear in the output circuit of the latter and in the grid circuit of the tube |02 as represented` in Fig. 18. The tube |02, similar to the tube 98, is so biased that any signals, more negative than those at the level represented at |62 in Fig. 18, are effective to drive this tube to cut off. In this amplier |10.

way, any of the undesirable signals referred to which are not removed by the tube `98 are eliminated by the tube |02. The output wave from the tube |02 will therefore be as represented in Fig. 19. This wave is comprised of the picture signals represented at |42, the signals represented at |44 and which have a duration approximately equal to t, and the signal represented at |52 and which has a duration equal to 12(T+t).

in Figs. 8 .and 9, and is applied as shown to the output circuit of the tube |02 and combine with the wave of Fig. 19 to produce the complete signal Wave as represented in Fig. 20. 'I'hls complete wave appears in the output connection 92 from the tube |02, and is supplied to a transmitter |68.

From the foregoing it will be understood that the signals represented at |44, |48 and |52, and which are applied to the grid circuit of the tube 96, make the undesirable signals represented at |46 and |50 suillciently negative to permit these undesirable signals to be eliminated by the tubes 98 and |02, as explained. The signals as represented at |44 and |48, also, are effective to cut ofi the ray during the periods of return deflection thereof in both the horizontal and vertical directions. In the complete wave as represented in Fig. 20, the signals vrepresented at |44 and |48 serve as pedestals upon which the synchronizing and framing signals appear, andthe latter are of the same polarity as and substantially greater in amplitude than the peak black picture signals. The receiving apparatus can therefore readily distinguish the picture signals from the synchronizing and framing signals by amplitude selection. It is to be noted that the synchronizing signals are of very short duration as compared with the duration of the signals as represented at |44, the period of duration of the synchronizing signals being only sufficient to drive the horizontal deflection circuit 30. Also, it is to be noted that the framing signals are of very short duration as compared with the duration of the signals represented at |52. The duration of the framing signals is only sufficient to effectively drive the vertical deection circuit 34.

An important vfeature of my improved system and method of operation resides in the fact that the synchronizing and framing signals are combined with the picture-signal Wave only after the undesirable signals, such as those represented at |46 and |50, have been removed. In the specic embodiment of my invention disclosed, this is accomplished by supplying the synchronizing and framing signals to the amplifier at a point beyond the two tubes 98 and |02.

The receiving apparatus shown diagrammatically in Fig. 21 comprises a radio receiver and A resistance |12 is connected across the output circuit of the receiver |10, and by a connection |14 from this resistance the Wave of Fig. 20 is applied to the control grid |16 of an electron gun |18, similar in construction and manner of operation to the gun |8 of the transmitter tube. The gun |18 is disposed at one end of the tube |80 and operates to develop and direct a ray |82 of electrons at a fluorescent screen |83 on the large end of the tube. Electromagnetic coils |84 and an associated horizontal deiection circuit |85, similar to thecircuit 30, operate to deflect the ray |82 horizontally at the rate of 7290 times a second.

Electromagnetic coils |86 and an associated The wave in the connection 88 from. the output of the amplifier 64 is as represented circuit'V |88, similarto the vertical denection circuit y94, operate lto deflect the ray vertically `at the rate of 60 times a second. The ray `|82 is therefore made to scan the screen |88 in the same manner and along the same pattern as the ray 20 scans thev screen I2 of the transmitter v'I'he incoming wave, as represented in Fig. 20, is applied to the input circuit of' a rectifier tube |90 which is biased to pass only the synchronizing and framing signals which are of substantially greater amplitude than' the peak black picture signals. f l

'Ihe synchronizing and framing signals are separated by a filter connected in the output circuit of the tube |90. This filter comprises a falling `in the spaces between the spaced hori-V zontal lines of the' thirty odd frames. During the return deflection of the ray |82 in the hori- V'zontal direction it is cut ofi' by the signals represented at |44 in Fig. 13, and during return deflection of the ray in the vertical direction it is cut oli by the signalsr represented at |52 in Fig. 14.

The intensity of the ray |82 is varied bythe picture signals to produce the image on the screen |83.

The'construction of the filter 65 lin the trans mitting apparatus is the same as the filter shown in the receiving apparatus.

The details of construction of the receiving apparatus may be made in accordance with the disclosure in the copending application by Arthur W. Vance, Serial No. 544,959. filed June 17, 1931.

The details oi' construction of the horizontal and

vertical deflection circuits

80, 34, |85 and |88 may be made in accordance with the disclosure in the copending application by Tolson et a1., Serial No. 595,484, filed February 27, 1932.

For the purpose of transmitting the direct current component referred to, I propose to employ a photoelectric cell 200 and support the same, as shown in Fig. l, adjacent the outer edge of the disc 40, between the disc and the film gate 48. In operation, as the pictures of the film pass through the gate 48, the light is reflected from the surface of the disc 40 to the cell 200, whereupon a current is developed whose amplitude varies proportionally with occurring variations in the average brilliancy or background of the amplifier 202, shown in detail in Fig. 22. As the current from the cell 200 flows through the battery 203 and the potentiometer 204 in Fig. 22,

the grid of the tube 206 is made more or less negative, depending upon the value of the current. This causes the plate current of this tube to decrease correspondingly through the rheostat 298 to cause the potential at the point 2| 0 to become more or less positive. This positive voltage is filtered by a condenser 2|2 and is connected as shown in Fig. l to the grid leak 2|4 of the tube |02, through a potentiometer 2|6 and a battery zlewnich'may b e used as an auxiliary manual controlwhendesired. f

In operatio'mthe bias ofthe ltub'e v| 02 is variedvl in accordance with" variations inthe average brilliancy or so-called backgroundbrilliancy of the]` pictures being transmitted, and vvthis action controls the heighth lor eiiectivevamplltude cfjthei synchronizing signals by varying theff voltage input to this tube at whichl cut oiIoccurs. Inother words, the amplitudev of the synchro`r nizingsignals; measured from'jtfhe A. C. axis' of l the entire wave as represented in Fig. 20varies transmitted proportionately with the background brilliancy of the object.' With proper provisions, made'at the receivingv station, the intensityfof the ray is varied so that the background Vo'raverage brilliancy of the reproduced picture varies with ocf curring variation of the background at the'object.

Since the details of construction of the rec'eiving'fl purpose are not part of my apparatus for this present nvention, no disclosure thereof hasbeen made.` 'Howeven tus capable of operating in this' manner and for the purpose' referred to is the copending application variation, the tubel 206 in ing level adjusted to vcorrect for the non-linearity a television receiving appara-'f disclosed in detaillnv by Ralph S. Holmes,

Serial No. 658,894, filed Februaryy 28, 1933. As av Fig. 22 may beoi' the i well known variable-mu type which has a very non-,linear characteristic, andjits bias and'work-l of the light vs. grid voltage vcharacteristic of the receiver tube |80. y

As a. modification, thefcell 200 may be supported to the left of the lensv 220. in Fig. 1 to receive the light reflected the light reflected from the disc 40. Also", the cell 200 may be supported therefrom instead of adjacent the tube |0 to receive the light from the screen |`2 when the object is an outdoor or studio scene.

It is important to note that in my improvedA system and method of operation the control wave, which provides for the so-called direct current component at the receiver, circuit of the tube |02. That is, this wave isy applied to the signal amplifier only after practically all of the undesirable signals referred to have` been eliminated by the tube 98, as explained.

As a, modification, the various sets of openings or slits in the single disc 54 may be made in as many differentdiscs, all fixed yon the shaft of the motor 56 and angularly related to produce the signals in the same way as the single disc. It will be understood that in such case the photoelectric cells and-the light sources will be associated with their respective discs.

is applied to the grid From the foregoing it will be seen that I^have provided an improved television system and method of operation thereof whereby it is possible to obtain the advantages of the so-called interlaced scanning action, Aand to maintain this action although there might occur somedegree of mistion, I believe myself to be the first, for this same purpose, to interrupt vthe framing signals and to pictures. This current is amplified in a D C adjustment which would otherwise interfere with e signals continuously to the circuit for defiecting 1 the cathode rays horizontally. In this connec- :analiticiv cause synchronizing signals to appear during the periods of interruption of the framing signals.

Further, it will be seen that by improved system and method of operation provision is made for the transmission of a control wave which can be utilized at the receiver to control automatically the background of the reproduced picture.

Further, it will be seen that by my improved system and method of operation the undesirable signals referred to are eliminated in at least two steps at the transmitter by employing signals to cut ofi' certain tubes during the periods of occurrence of the undesirable signals.

While but one embodiment of my invention has been disclosed, it is understood that various modiflcations, within the conception of those skilled in the art, are possible without departing from the spirit of my invention or the scope of the claims. s f

I claim as my invention:

1. In the art of television, the method of operation which comprises developing synchronizing signals at a, relatively high line-scanning frequency and framing signals at arrelatively low framing frequency, amplifying said signals, and causing the synchronizing signals to occur at a frequency substantially greater than the linescanning frequency only during substantially the periods of occurrence of the framing signals.

2. In a system for communication by television, a scanning device for developing picture signals, means for causing scanning action of said device at a given uniform rate, a multi-tube electrical circuit supplied with picture signals from said device, means supplying a tube of said amplifier with signals occurring at said rate and each of the same polarity as and greater in amplitude than any of the picture signals representative of conditions of shade at the object, and means supplying to a tube between said first-named tube and the output tube of said circuit control signals occurring at said rate and being of the same polarity as and in phase with said second-named signals.

3. In a system for communication by television, a scanning device for developing picture signals, means for causing scanning action of said device at a given uniform rate, a multi-tube electrical circuit supplied with picture signals from said device, means for supplying to said circuit a first set of control signals occurring at said rate, at least one of the tubes of said circuit being cut off by each of the control signals, and means for supplying to said circuit a second set of control signals of the same polarity as and in phase with the rst set of control signals, each of the signals of the second set being of shorter duration than those of the rst set.

4. In a television system, a scanning device, means for causing scanning action of said device, means for developing and supplying to said firstnamed means control signals at a relatively high line frequency and other control signals at a relatively low framing frequency and with the individual framing signals interrupted and with signals at the relatively high frequency occurring during the periods of interruption of the framing signals, said second-named means comprising a light-sensitive device, a light source, a rotatable member for controlling the manner of illumination of said light-sensitive device by the light source and for interrupting the light at least once during the periods of occurrence of the individual framing signals, and means for rotating said member in time with the frequency of occurrence of the framing signals.

5. In a television system, a cathode ray scanning device provided with a screen, means for developing a ray of electrons and directing the ray at said screen, means for deflecting the ray in one direction at a,relatively high frequency and means for simultaneously deecting the ray in a different direction at a relatively low frequency to cause the ray to scan said screen, means for generating and supplying synchronizing signals at the relatively high frequency to said secondnamed means and framing signals at the relatively low frequency to said third-named means, with the individual framing signals interrupted and with some of the synchronizing signals occurring during the periods of interruption of the framing signals, and ,an amplifier for amplifying the synchronizing and framing and picture signals.

6. In a television transmitting system, a scanning device for developing picture signals, a multitube amplifier for amplifying the picture signals, means for generating electrical signals at a given frequency and applying the same to a tube of said amplifier under conditions whereat these signals are of the same polarity as the picture signals representative of conditions of shade at the object being transmitted, the amplitude of said electrical signals being suicient to" bias said tube to cut oif, and means for generating control signals at said given frequency and applying the same to a tube of said amplifier under conditions Whereat these signals are of the same polarity as said electrical signals.

7. In a television transmiting system, a scanning device for developing picture signals, a multi-tube amplifier for amplifying the picture signals, means vfor generating electrical signals at a given frequency and applying the same to a tube of said amplifier under conditions whereat these signals are of the same polarity as the picture signals representative of conditions of shade at the object being transmitted, the bias on said tube being at a value to permit passage through the same of substantially all of the picture signals at said polarity, the amplitude of said electrical signals being sufficient to bias said tube to cut ofi", a second tube supplied from said first tube with said electrical signals at said polarity and biased to pass substantially all of the picture signals at said polarity and to be cut oif by said electrical signals, and means for generating control signals at said given frequency and applying the same to a circuit in said system on the output side of said second tube and under conditions whereat these signals are of the same polarity as said electrical signals.

8. In the art of television transmission, the method of operation which comprises generating a picture-signal wave, generating and adding to said wave electrical signals occurring at a given frequency and which are of the same polarity as the picture signals representative of conditions of shade at the object and at least of the same amplitude as the peak picture signals of said polarity, and generating and adding to said wave control signals at said polarity and which occur in phase with said electrical signals.

9. In the art of television transmission, the method of operation which comprises generating a picture-signal wave, generating and adding to said wave electrical signals occurring at a given frequency and which are of the same polarity as the picture signals representative of conditions of shade at the object and at least of the same amplitude as the peak picture signals of said polarity, and generating and adding to said wavel control signals at said polarity and which occur in phase with said electrical slgnalsjand which are of shorter duration than the latter.

l0. In the art of television transmission,`tllie methodl of operation which comprises generating v a picture-signal wave, generating and adding to, said wave electrical signals of the samepolarity as'the'picture signalsrepresentative of conditions of shade `at the object and at least of the same amplitude as the peak picture signals of said polarity, some of said signals occurring at a relatively high synchronizing frequency and othersY occurringat a relatively low framing frequency, generating and adding to said wave control signals at said polarity and which occur in phaseV with the electrical signals at said relatively high frequency, and generating and adding to said given frequency, means for generating control signals at said frequency, a multi-tube amplifier for the picture signals, means for generating blanking signals and for applying them to one of the tubes of said amplifier, means for developing a signal wave which varies in accordance with occurring variations in overall brilliancy of the object being transmitted, a connection for applying the signal wave to the grid circuit of a tube of said amplifier which is subsequent to said one tube, and a connection for` applying the control signals to said amplier on the output side of said last-mentioned tube'.

12.1In a television transmitting system, a scanning device for developing picture signals, means for causing scanning action of said device at a given frequency, means for generating control signals at said frequency, a multi-tube amplifier for the picture signals, means for generating blanking signals and for applyingthem to one of 'the tubes of said amplifier, means for developing a. direct current which varies in accordance with occurring variations in overall brilliancy of the object being transmitted, a connection for applying the direct current to the grid circuit of a tube of said amplifier which is subsequent to said one tube, and a connection for applying the control signals to the amplier on the output side of said last-mentioned tube.

13. In a television transmitting system, means for generating horizontal scanning synchronizing impulses, means for generating vertical scanning synchronizing impulses each of longer time-duration than a horizontal synchronizing impulse, means for interrupting the continuity of each vertical synchronizing impulse, amplifying means for said impulses, and means for introducing into the system a horizontal synchronizing impulse during each interruption period whereby, at a receiver, the periodicity of the horizontal synchronizing impulses is not impaired.

14. In a television transmitting system, means for generating horizontal scanning impulses, means for generating vertical scanning synchronizing impulses at a frequency incommensurable with the frequency of the horizontal impulses and means for periodically increasing the inte` grated energy-content of the horizontal impulses at time periods immediately before the occurrence of the vvertical whereby.

integration. in a receiving device, the ,energyl contentof each` vertical impulse is substantially., the same as that of every other verticalinipulse. t

`15. Control apparatuscomprising,means fordeveloping vcontrol 4signalsv at .a relativelyA high frequency, means for developing control signals@l at a relatively low frequency and .with the lindividual signalsat the relatively low frequency` interrupted, and meansforr supplying Van elec-- tricalfcircuit with said highfrequency signals` and said lowfrequencygsignals at-,the same 1 polarity with respect to each other and with some.,

of the signals at the relatively high frequency occurring respectively during f the periods of inf terruption of the signals vat Athe relatively low frequency. v j ,Y g, Y

16. Control apparatus comprising means ffor developing control signals at a relatively high frequency, means for developingv control signals at a relatively low frequency. and with the rio" individual Signals at the relatively low fre-fquency interrupted for arperiod greater than the period of occurrence of the individual signalsat f thev relatively high frequency, and means for supplying an electrical circuit with said lhigh,

frequency signals .and said low frequency sg-` nals at the same polarity with respect to eachother and with some of the signals at the relatively high frequency occurring respectively during the periods of interruption of the signals at lthe relatively low frequency. y

17. vIn a television system comprising a scan- 'f ning device for obtaining scanning action at a relatively high rate kof m lines per second and z a relatively low rate of n frames per secondff an electrical channel for amplifying synchronizi-v ing signals effective at the rate of m times per 1 second and for amplifying framing signals effective at the rate of n times per second, means for developing and supplying the synchronizing signals to said amplifier channel, and means for developing and supplying the framing signals to Y said amplifier channel and in an interrupted fashion during each framing period with at least some of the interruption periods in phase` with the periods of occurrence of they synchronizing signals.

18, In the art of television, `the method of* operation whichy comprises developing av synchronizing signal which recurs at high frequency, developing an interrupted frama relatively Y ing `signal which recurs atarelatively low fref quency` with the interruption .periods in phase with and of greater durationthan the periods of occurrence of the synchronizing signals, 'and amplifying said signals.

19. Inthe art of television, the method ofy being equal to :v-I-y, a: being a whole number and y being less than one, and developing additional signals which are similar to the synchronizing signals and which occur only during substantially the periods of occurrence of the framing signals at the frequency of at least m per second 'region of saidlpicture signals, means for clipping and in such time relation to the synchronizing signals that the effect is produced of having synchronizing signals occur at the rate of at least 2m per second.

20. In a television system, a scanning device, means for causing scanning action of said device, means for developing synchronizing signals at a relatively high line frequency and framing signals at a relatively low framing frequency with the individual framing signals interrupted and with the synchronizingy signals occurring during the periods of interruption of the framing signals,'and means for supplying said signals to said first named means.

21. In a television system including means for generating picture signals periodically, there being undesired signals generated 'at the end of each period of picture signal generation, the method of operation which comprises so changing the amplitude location of said undesired signals that they are removed from the region of said picture signals, clipping off said undesired signals whereby4 a pedestal is produced at the end of each of said periods, and adding a synchronizing impulse to the top of each of said pedestals.

22. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of each period of picture signal generation, means for so changing the amplitude location of said undesired signals that they are removed from the region of said picture signals, means for clipping oil said undesired signals whereby a. pecl, estalis produced at the end of each of said periods, and meansfor varyingthe heighth of said pedestals in accordance with the average illumination of the image being transmitted.

23. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of each period of picture signal generation, means for so changing that amplitude location of said undesired signals that they are removed from the region of said picture signals, means for clipping off said undesired signals whereby a pedestal is produced at the end of each of s aid periods, means for varying the heighth of said pedestals in accordance'with the average illumination of the image being transmitted, and means for generating synchronizing impulses and for adding one of said synchronizing impulses to the top of each of said pedestals. a

24. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of'each period of picture signal generation, means for so changing the amplitude location of said undesired signals that they are removed from the region of said picture signals, means for clipping off said undesired signals whereby a pedestal is produced at the end of each of said periods, means for varying the heighth of said pedestals in accordance with the average illumination'of the image being transmitted, and means for generating synchronizing impulses which are narrow as compared with the width of said pedestals and for adding one of said synchronizing impulses to the top of each of said pedestals.

25. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of each period of picture signal generation, means for'so changing the amplitude location of said undesired signals that they are removed from the oif said undesired signals whereby a pedestal is produced at the end of each of said periods, and means for increasing the heighth of said pedestals in response to an increase in the average illumination of the image being transmitted.

26. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of each period of lpicturejsignal generation, means for producing blanking impulses which occur at the same time as said undesired signals, means for adding said blanking impulses and said picture and undesired signals whereby said undesired signals are removed from the region of said picture signals, means for clipping o2 said undesired signals whereby a pedestal is produced at the end of each of said periods, means for producing synchronizing impulses which occur at the same time as said pedestals, and means for adding said synchronizing impulses to said pedestals.

27. In a television system for the production of pictures at a certain frame frequency and at a certain scanning line frequency, means for producing interrupted rectangular impulses occurring at said frame frequency, means for producing rectangular impulses occurring at a frequency which is a multiple of said scanning line frequency and which have a Width which is less than the width of said interruptions, and means for so combining said interrupted impulses and said multiple `frequency impulses that said multiple frequency impulses are located in said interruptions. i

Y 28. In the art of television, the method of operation which comprises developing a synchronizing signal which recurs at a relatively high frequency of m per second, developing an interrupted framing signal which recurs at a. relatively low frequency of n per second with theinterruption periods of the framing signals occurring in phase with and being of greater duration than the periods of occurrence of the synchronizing signals,

being equal to a whole number plus k being a whole number less than 8,"and developing additional signals which are similar to the synchronizing signals and which occur only dur- .ing substantially the periods of occurrence of the being equal to a whole number plus k being a whole number less than 8, and means for periodically increasing theintegrated energy rso producing a rectangular voltage impulse `at the end of each period vof `picture signal generation, means for producing synchronizing voltage impulses which occur at the same time as and which are narrower than said rectangular impulses, arid means for so adding said picture signals, said rectangular impulses and said synchronizing impulses that a synchronizing impulse is located on the top of each rectangular impulse.

3l. In a television system including means for generating picture signals periodically, there being undesired signals generated at the end of each period of signal generation, means for' so changing the amplitude location of said undesired signals that they are removed from the region of said picture signals, means for clipping off at least a portion of said undesired signals whereby the position of the alternating ciu'rent axis for the picture signals and the undesired signals is changed, and means for again clipping oi at least a portion of said undesired signals.

32. In television apparatus, means for producing horizontal synchronizing impulses which occur at a relatively high frequency, each of said impulses having a front or leading edge, and means for producing framing impulses which occur at a relatively low frequency and which have l slots therein that have a back or trailing edge which occurs in the same time relation as said leading edges whereby the time intervals between the successive above-mentioned edges are the same. f

33. In television apparatus, means for generating horizontal synchronizing impulses which occur at a relatively high frequency, each of said impulses having an edge which changes abruptly in a certain direction with time, and means for generating framing impulses which occur at a relatively low frequency and which have slots therein that have an edge which changes abruptly in said certain direction and which occurs in the same time relation as the said edges of said horizontal synchronizing impulses whereby the time intervals between the successive above-mentioned edges are the same. i

34. The invention according to claim 33 characterized in that additional means is provided for generating during the periods immediately preceding each framing impulse impulses which occur at a rate which is a multiple of the frequency at which the horizontal synchronizing impulses occur.

35. In a television system, means for scanning a view to be transmitted and developing picture signals, means for transmitting a horizontal synchronizing impulse at the end of each scanning line, said impulse having an edge which changes abruptly in amplitude in a certain direction with respect to time, means for transmitting framing impulses at the end of each picture frame which impulses have slots therein having an edge which changes abruptly in amplitude in said certain direction with respect to time and which occurs in the same time relation as the said edges of said horizontal synchronizing impulses whereby the time intervals between the successive abovementioned edges are the same.

36. The invention according toclaim 35characterized in that lthere is .additional means'for producing' auxiliary impulses which` occur during the periods immediately preceding and'f immediately following each framing impulse and which in combination with the horizontalsynchronizing impulses form a group of regularly recurring impulses.

37. In a television system, means for generating horizontal synchronizing impulses which occur at a relatively high frequency, means for generating slotted framing impulses which occurat a relatively low frequency, and means for generating a group of impulses immediately preceding each framingimpulse which impulses occur at arate which is a multiple of the frequency at which said horizontalv synchronizing impulses occur, said-slots occurring at said multiple frequency and the trailing edges of said slots occurring in the same time relation as the leading edges of said impulses in said group of impulses. v

38. The invention according to claim 37 characterized in that said last means includes means for making at least one of the impulses in said group of a diiferent width or duration than the other impulses in said group. f

39. The invention according to claim 37 characterized in that said last means includes means for generating a group of impulses immediately following each framing impulse which impulses occur at a rate which is a multiple of the fre- -quency at which said horizontal `synchronizing impulses occur, said last mentioned impulses having leading edges which occur in the same time relation as the trailing edges of said slots.

40. In a television system, means for generating horizontal synchronizing impulses which occur at a relatively high frequency, and means for generating groups of framing impulses which groups occur at the relatively low framing frequency, each of the impulses in one ofy said groups following one of said horizontal synchronizing impulses.

41. In a television system, means for generating horizontal synchronizing' impulses whichl occur at a relatively high frequency, each of said impulses having a front or leading edge, and means for generating framing impulses which occur at a relatively low frequency and which have evenly spaced slots therein that have a back or trailing edge, the back or trailing edge of each alternate slot occurring in the same time relation as the said leading edges whereby the time intervals bequency, developing an interrupted framing signal which recurs at a relative low frequency with the interruption periods `in a flxed'phase relation to the periods of occurrence of the synchronizing signals.

44. A method of providing synchronizingsignais for use at a television receiver employing interlaced scanning, said method comprising generating line synchronizing pulses, generating 7g groups of pulses, each of which groups constitutes a. frame signal, causing said groups of pulses to provide, during at least the earlier part of each of said frame signals, leading edges which occur at n times the frequency of said line pulses where n is a small integer representing the number of traversals in which the object to be transmitted is completely scanned, causing certain of said leading edges to occur in phase with the leading edges of said line pulses, so that leading edges occur at line frequency throughout .said synchronizing signals, and transmitting said line pulses and frame signals.

45. A method according to claim 44, in which said line pulses and the pulses constituting said frame signals aregenerated with a substantiallyr rectangular wave form.

46. A method of providing synchronizing signals for use at a television receiver employing interlaced scanning, said method comprising generating line synchronising pulses in the intervals between trains of picture signals representative of lines of the object to be transmitted, generating auxiliary line pulses occurring-at n times the frequency of said line pulses where n is a small integer representing the number of traversals in which said object is completely scanned, causing every nth leading edge of said auxiliary line pulses to occur in phase with the leading edges of said line pulses, transmitting said line pulses during traversals of said object and transmitting said auxiliary line pulses between successive traversals of said object.

47. A method according to claim 46, in which 'said line pulses and said auxiliary line pulses are generated with a substantially rectangular waveform.

48. A method according to claim 46, in which said line pulses and said auxiliary line pulses are generated with substantially the same amplitude.

49. A method of providing synchronizing signals for use at a television receiver employing interlaced scanning, said method comprising generating line synchronizing pulses in the intervals between trains of picture signals representative of lines of the object to be transmitted, generating frame synchronizing signals having a duration greater than the interval between successive line pulses, suppressing parts of said frame signals for forming in at least the early part of each frame signal leading edges which occur at n times the frequency of said line pulses where n is a small integer representing the number of traversals in which said object is completely scanned, causing certain of said leading edges to occur in phase with leading edges of said line pulses, and transmitting said line pulses and frame signals.

ALDA V. BEDFORD. N