US2398642A - Method and system for television communication - Google Patents

Description

April 3946. J. H. HOMR IGHOUS 2398,42 METHOD AND SYSTEM FOR TELEVISION COMMUNICATION Original Filed May 13. 1940 4 snags-sheet 1 Moo. POWER AME AM]? osc. 7, ,BLANK- n FREQ.

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MOTOR April 16, 1946. i I H. HOMR|GHO U$ 2,393,542

METHOD AND SYSTEM FOR TELEVISION COMMUiiICATION I Ori inal Filed May is, 1940 4 Sheets-Sheet 2 April 16, 1946. J. H. HOMRIGHOUS METHOD AND SYSTEM FOR TELEVISION COMMUNICATION 4 Sheets-Sheet 3 Original Filed May 13, 1940 HALF WAVE

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FIGI5 April 1 1946- J. H. HOMRIGHOUS 8,

METHOD AND SYSTEM FOR TELEVISION COMMUNICATION Original Filed May 13, 1940 4 Sheets-Sheet 4 Petente METHOD AND SYSTEM FOR TELEWSIQN coma CAEEQN John H. Homrighous, Oak Park, Ell.

()riginal application May 13, 1M0, Serial No. 33%,36d, new lfatent Rio. 2,32il,699, dated dune l, 19%. Divided and this application September 17, 19. .2, Serial No. 458.612

19 (Claims.

My invention relates to improvements in methocls and systems for television communication and particularly to systems for producing synchronizing signals for controlling and timing the various impulses required for the production of a picture at both the transmitter and receiver.

One of the objects of my invention is to provide an improved cathode ray deflecting system for producing interlace scanning by applying a different electrical condition to the vertical deflecting means in alternate fields or by changing the time interval of every other field.

Another object of my invention is to provide a synchronizing signal generating mechanism for producing the various impulses necessary for the control of scanning in a cathode ray tube with provision for adjusting the speed of the mecha nism to develop substantially-wide frequency range of impulses. v j

Another object of my invention is the provision of synchronizing signal mechanism at the receiver which permits greater flexibility so that such mechanism may respond to signals representing different picture rates and also different number of lines per picture.

One of the main objects of my invention is an improved method of alteringthe number of picture changes or frames in a given time in order to televise motion picture film at 24 frames per second, or, the standard for television practice of 30 frames per second, or at any other desired number of frames per second.

Another object of my invention is the provision of a switching device for changing the number of horizontal lines per field or frame without changing the frame frequency.

Another object of my invention is the provision of an element in the cathode-ray picture tube to initiate pulses of current to be used for. blanking purposes or for reducing the intensity of the electron beam duringthe retracing period or backward movement;

Another object of my invention is the provision of elements in the cathode-ray reproducing tube to initiate pulses of current to blank or reduce the intensity of the electron beam during the retracting period.

Another object of my invention is the provision of means for automatically adjusting the lines horizontally in each image field.

Another object of my invention is the provision of means sensitive to variations of lightin the reproduced images for controlling the brightness of the images.

A feature of my invention is the generation of mission of this wave to the receiver whereby the same wave form and frequency may be regenerated and other frequencies may also be generated from the source of power at the receiver. 1

Several methods for producing interlace scanning have been devised. One system, known as the even line system, requires that the up and down movements of the cathode ray be of unequal length, which has been very difiicult to obtain. In my present invention, I have devised a more positive method for developing control impulses siving alternate short and long spaced periods of time. Another system, known as the odd line method, has been devised which requires a whole number of lines plus a fraction of a line in each field so that the electron ray will start the second field at a fraction of a line distant from the start of the first line in the first field. This system depends upon equal field length and exactly alike vertical deflecting means for all fields. In the preferred embodiment of my invention I employ different intervals to the vet-ti I cal deflecting means in alternate fields to shift the electron ray vertically the distance equal to the space of one horizontal line. In none of the present systems can the number of pictures in a given time be changed from 24 to 30 pictures to televise motion picture film at a much lower rate, 24 frames per second, than the proposed standard rate for television, 30 frames per second, as described further along. None of the above systems show elements added to the cathode-ray tubes to'initiate voltage pulses for blanking purposes. I

In my prior application Serial No. 306,537, filed November 28, 1939, the picture signals are combined with control and sound or audio signals in such a manner that all three are transmitted and reproduced as picture or video signals.

According to a preferred embodiment of my present invention, a voltage wave at the frame frequency is generated at the transmitter, and combined with the audio signals on a separate intermediate carrier frequency, which in turn is modulated on the video carrier frequency and transmitted by radio to the receiver.

Another advantage of my invention is the genoration of blanking pulses by the pick up and viewing tubes, thereby eliminating the transmission of these signals filtering equipment. I

Other objects, features and-advantages ofmy invention will appear from tion taken in connection with the accompanying by radio and the necessary.

thefollowinp descripdrawings, illustrating an embodiment thereof in which:

Figures 1 and 2 are simplified diagrammatic view of a television transmittin station and a television receiving station, respectively, illustrating theprinciples applied in this invention.

Figure 3 is a motor driven device for generating control frequencies.

Figures 4 and 5 are end views of the disks shown in Figure 3 for generating the control or frame frequency.

Figure 14 shows an end view of disk used in Figure 13.

Figure 15 shows picture control character, reproduced at the receiver.

' Figure 16 shows my improved cathode-ray pick up tube with circuit connections.

Figure 17 is a top view of the mosaic used in tube shown in Figure 17.

Figure 18 shows my improved cathode-ray viewing tube with circuit connections.

In Figure 1, the numeral i designates a cathode-ray pick up tube of the conventional type and is known as an Iconoscope." It is to be understood that other tubes such as Orthiconoscope developed for perpendicular scanning'of all points on the mosaic, or the tube known as the image dissector may be used instead of the one illustrated. As shown, the tube comprises a mosaic, photoelectric screen on which a li ht image of the object is projected and produced, having two metallic plates on the opposite side, and an electron gun for generating a rayof electrons directed at the screen, and two sets of deflecting plates for defiectingthe electron ray at the'line and field frequencies, so that it is caused to scan the screen. The picture and certain other control characters are thereby developed and fed from one of the metallic plates by an output connector 2 to a modulating amplifier 3. The other connector 4 leads to a blanking pulse circuit 5 to be further described in connection with' Figure 12. v

A carrier wave is provided by an oscillator 6 in the power amplifier 'l. Thisvcarrier now is modulated by the frequency band video or picture signals through the modulation amplifier 3. The signals from the amplifier I are supplied by a connection 8 to the mixing circuit 3. Certain control signals are also transmitted as video signa1s.-

The numeral l0 designates a generator for producing pulsating voltage waves or waves of sine form for controlling the sweep frequencies at the desired frame frequency. The low frequency sweep control voltage waves or signals through the medium oi amplifier ii, modulates another carrier produced by oscillator i2 in its amplifier. stage l3.

The audio or sound signals from the microphone I4 are passed through an amplifier IS.

The sweep control signals and the audio s18- nalsare applied through a .mixer circuit ii to modulate a second main carrier wave in the power amplifier stage II produced by the oscillator iii. The signals from the amplifier H are fed The two carrier waves, one, modulated by sweep I frequency control signals and audio signals, the other, modulated by video signals are mixed in the mixer circuit 9 and fed to the common antenna 23 for transmission by radio.

The sweep control signals are transmitted in the form of sine waves, which are used to synchronize or control the scanning action with the transmitter.

The antenna 2i receives the combined carrier signals from the transmitter antenna 20 to a radio frequency amplifier 22, an oscillator it reacts with these signals in the first stage 24 on the superheterodyne principle, to produce two intermediate-frequency signals which are fed to the two stages 25 and 26.

After suitable amplification, the video signals are detected at 21 and fed by a connection 23 to a reproducing device 29. The device 2! is represented as being in the form of a cathode-ray tube of well known construction, and comprises a fluorescent screen, an. electron gun for developing a ray of electrons directed toward the screen, and two sets of electrostatic plates for deflecting the electron ray at the line and field frequencies to cause it to scan the screen. It is to be un- 26 which contains the sweep signals and the audio signals and through the action ofwthe second detector 30 the output of which goes to two selective filters 3| and 32. The low frequency sweep control signals after leaving the filter 3|, still in modulated form on a carrier are demodulated at 33 and fed to the frequency generator 34 where the signals may be amplified and operate a signal generator to redevelop control signals, or the signals may be used after suitable amplification to directly control the scanning action at the receiver which will be explained in more detail later.

The audio signal from the filter 32 is fed to the loud speaker 35. The numeral 36 represents what may becalled an automatic brightness control circuit and derives its energy from the changes in brightness of a spot or mark 31 televised from the transmitting tube and directed into a photocell circuit. The output from this circuit is used to adjust the bias on previous stages to aid in maintaining the brightness of the reproduced picture substantially constant.

Referring to Figure 3, the numeral 33 represents a motor which is operated from the local suppLv current and normally runs at approxi- Y mately 1800 R. P. M. Operated from the motor to the mixer circuit 9 through the conductor I3. The revolving and stationary members are bet- The video si ter shown in Figures 4 and 5. In Figure 4 the disk 52 is made up of two halves of polarizing material: each half may be rotated through a very small angle and as shown on the drawing the planes of polarization are not parallel. This angle depending upon the desired size of the dark portion 49 or the period of the gap between pairs of pulses as illustrated at 50.

From the above it will be seen that when the disk 42 is rotated past the stationary member 45 and between its source of light 48 and photoelectric cell I that the intensity of the light reaching the photo-cell will vary from zero to maximum value and back to zero when rotated through aproximately 180 degrees.

Referring to Figure 5, the numeral M represents a disk of light polarizing material having a certain part painted or blacked out so that rotating it in a clockwise direction past its stationary polarized member 43 and 44 and between its sources of light 46 and 41 and their respective shown in Figure 3. These photo-cells control the photocells 52 and 58 the intensity of light reach-) ing each photo-cell will vary from zero value to maximum value and back to. zero during one half of a revolution and during the other half of the revolution there will be no light change.

A system for producing the'proper sweep voltages and control signals is shown in'Figures 8 to 12 inclusive. In Figure 8 I have shown a photocell 54 which may be the photo-cell 5| in Figure 3. This cell is responsive to the variations of light intensity caused by the rotation of disk 42 previously explained to cause grid excitationof amplifier 55. The anode of tube 55 is connected through the primary winding 56 of a transformer to the positive-terminal of the voltage divider 51 to thereby produce pulsating voltages for. controlling the discharge tube. To produce the desired output wave of saw tooth form for field scanning I employ a grid controlled discharge tube circuit shown in Figure 9, where the pulsating voltages from transformer winding '56 are induced into the transformer secondary winding to drive the grid of tube 58 positive, discharging the condenser 59 through the tube 58. Thus by alternately charging the condenser 59 through the resistance 50 and discharging it through the tube 58 a saw tooth voltage is generated.- The vertical sweep. pulses generated :by the wave forming circuits Figure 9 is fed to conductor 6| at the transmitting tube Figure 1 and as diagrammatically shown in Figure 6. The circuit of Fig ure 9 is also used to produce the line sweep voltages.

From the above description it will be seen that each revolution of the disk 42 will produce two similar impulses in the transformer winding 58 to trigger the discharge tube 58. The tube 58 may be biased so that only the positive pulses applied to the grid will operate the tube. Since there is a gap 49 in the disk 42 successive impulses will occur at diflerently spaced intervals. Changing the speed of the disk by the adjustment of the cone pulley 89 will change the pic.- ture rate without changing the number of lines per picture. a The control voltages produced in Figure 8 may be transmitted to the receiving station to govern the scanning thereat.

The pulses generated bythe disk 42 can be used to produce the line scanning control pulses by interposing frequency multipliers between the circuits of Figures 8 and 9. I may also use disk 4| having associated with it two sources of light 46 and 41 and their respective photo-cells 52 and light intensity caused by the rotation of the disk 4| as previously explained.

Referring to Figure 11, I have shown a circuit for producing an alternating current from the variation. of light occurring in the photo- cells 62 and 63 which may be the photo- cells 52 and 53 former 69 to the positive side of voltage divider 10. The cathodes Hare connected in parallel to an intermediate point of the voltage divider Ill. The cathode 13 of photo-cell 62 is connected to the grid 64 of amplifier 56 and through re-' sistance 14 to negative potential at the voltage divider, thereby maintaining the grid 66 at a negative potential with respect to cathode H and plate 68; the circuit is so arranged that an increase in the intensity of light on the photo-cell 62 will increase the current of tube 66. The photo-cell 63 has its anode 15 connected to the grid 65 of amplifier tube -6 and it is maintained at a positive potential with respect to its cathode 16. This causes a decrease in the-current of tube 61 upon increasing the intensity of light directed toward the photo-cell 53. Other amplifier tubes may be connected in parallel to increase the amplification.

Therefore, since the plates of tubes 56 and 61 are in parallel, the rotation of, the disk 4| will alternately operate the photo- cells 62 and 63 to produce continuous rising and falling current in the transformer primary winding 69, whereby, alternating voltages are induced in the secondary winding. These control voltages from winding 69 may be induced into the transformer winding of Figure 9 to control the vertical deflection,

and by changing the speed of rotation of the disk 4| the duration of the time per field is changed so that any desired number of frames per second may be produced.

One method or system for producing interlace' scanning uses the disk 4|, Figure 5 with Figure 11, to develop impulses/to trigger the sweep generator, Figure 9, to thereby control the vertical reciprocating movement of the electron ray at different time intervals whereby one field period will be of a, greater duration than the next succeeding field since the dark portion on disk 4| extends through more than an degree are. Therefore, the return trace time in alternate fields will be greater than in the intervening fields, causing a fractional part of a line to be included in each field, which will have the efiect of placing the lines of alternate fields between those of intervening fields.

From the above it will be seen that I have devised a novel method of producing unequal field constitute the frequency generator shown at It, I

Figure 1.

It is proposed to use frequency multiplying circuits for the purpose of producing the high frequency required for horizontal line scanning.

The field frequency is obtained as described above and from these frequencies the higher line fre-- quencies are produced.

Referring to Figure 10, two stages of frequency multiplication are shown. The secondary winding I8 is connected to the transformer winding 88 in Figure 11 whichsupplles alternating pulses to the taped secondary and in turn to the full wave rectifier tube I8 which delivers twice the number of pulses or cycles to the tuned filter comprising the condenser 88 and the next transformer primary winding 8|. This double cycle signal is supplied by the taped secondary 82 to the full wave rectifier 83 where it is again doubled and fed to the next succeeding transformer-primary 84. The taped secondary 85 delivers alternating current to the next stage and so on until the desired high frequency for line scanning is obtained. While I have shown a circuit to double or to multiply the frequencies, other frequency multiplying circuit may be used.

'In my invention I prefer to use the doublers and obtain 128 or 256 lines per field, where each field will have exactly the same number of pulses, therefore, the same number of lines for each field and to avoid interference with local power, all that is necessary to do is to change slightly the field rate, which will of course change the line frequency but will not change the number of lines per field.

With reference to Figure 7, I have provided two switches 88 and 81 for shorting out one or more stages of doublers; for instance, certain stations could be operating on 256 lines per field and other stations on 128 lines per field.

In order to produce or develop interlaced scanning from a sine form voltage wave it is necessary to identify every other field pulse and in some manner cause the horizontal lines of one field to fall in between the lines produced in the other field or the lines of one field are even numbered and in the second field they are odd numbered. I-accomplish these features by the circuit shown in Figure 12. In this circuit, voltage waves of sine form are supplied from the circuit,

of Figure 11 to a full wave rectifier 88 of conventional design, which may be one stage of Figure 10. The output wave form is shown at 81; these pulses are fed through the transformer winding 88, which may be the winding 81 in Figure 10, to wave forming circuit Figure 9 to drive the grid of tube 58 positive discharging the condenser 58, thereby producing saw tooth form waves for vertical scanning as previously described. Inductively connected with the transformer winding 68 in Figure 11 is a half wave rectifier 88, the output wave form is shown at 88.

The current in the half wave rectifier load can be adjusted to impress voltage pulses on the grid of tube 8| out of phase with the voltage pulses developed in the full wave rectifier 86. The anode of amplifier 8| is connected through the primary transformer winding 82 to battery. The current pulses in the primary winding 82 .will induce in the secondary a voltage which will alter the potential in conductor 93, from that furnished by the battery, for the duration of each pulse and in phase with the vertical sawtooth voltage waves. The conductor 83 supplies potential through a centering resistance to one vertical deflecting plate. ing plate is supplied with potential from the same source through another centering resistance not shown. The potential on the plate of ampllfier 8| is adjustable, depending upon the space between lines.

The rectifier and amplifier 8| will operate during each positive pulse to increase or decrease the potential on one of the deflecting plates without changing the potential on the opposite plates, which will have'the effect of raising or lowering the horizontal lines.

From the above description it will be seen that I have provided a novel and very simple means for interlace scanning or for shifting the position of the horizontal lines scanned .in a cathode-ray tube, during alternate field pulses and which are controlled by the generator at the transmitting station. Thus eliminating the necessity of transmitting by radio synchronizing pulses other than the one sine form wave. Y

At the receiver I employ thesame means for identifying the positive pulses and at the same time causing the shift in the position of horizontal lines on the viewing tube screen.

The circuit figure number shown inFigure 7, omitting Figure 11, may constitute in one receiving station the frequency generator shown at 34, Figure 2.

From the above description it will be seen that the line pulses are definitely locked with the field pulses, or in other words, the same pulse that triggers the vertical deflection also supplies through multiplying circuits the trigger pulses for line scanning.

Furthermore, from the above description, the control of the field and line deflecting circuits at the receiver from the sine form voltage wave transmitted by radio from the transmitting station will cause the cathode-ray or electron ray at the viewing tube to be in exact synchroniza tion with the cathode-ray in the pick up tube, whenever the receiving station is tuned to the proper carrier wave.

In other words, at any time or interval that the I 48, than since a single frequency or control volt-" age wave generated at the transmitter station times the deflection of both the-field and the horizontal lines at both the transmitting station and reeciving station, the cathode-ray at the viewing tube would automatically be focused at the midpoint of line 40 on the screen of the viewing tube, and furthermore since I have provided through the medium of a half wave rectifier, Figure 12, means for associating the positive pulse in each cycle of the control voltage wave with a certain field, the focused electron ray in each tube would also fall in the proper field. The picture produced from this system will be approximately as' high as they are wide, since there isno necessity of reserving space at the bottom of picture for synchronizing pulses.

The other vertical defiect- Another system for controlling the scanning operations at the receiving station may comprise the motor 84, Figure 13, having control circuits for keeping the position of the rotor in step with the alternating current signals. The motor 84 drives disks or mechanisms similar to those explained in connection with Figure 3 to in turn develop line and field trigger potentials, utilizing the circuits shown in Figure 7. The motor and mechanism shown in Figure 13, together with the circuits shown in Figure 7 may constitute the frequency generator 35, Figure 2, in another receiving station. The power amplifier 85 may be supplied with signal current from the detector 33, Figure2. These signals, after proper amplification at 95, are fed to the motor 9t through contact 96 and 91. The half wave rectifier 98 will supply the positive pulses to one winding of relay 99. The motor 9% is small and carries a very light load; therefore very little power is required to operate it. Secured to its shaft are three disks of polarizing material, two of which are exactly like those shown in Figures 4 and with-their associated stationary polarized members and photo-cells. The disks are designated by the same numbers M and t2 and operate the circuits shown in-Figure 7, as previously explained, in connection with the transmitting station. In the preferred embodiment of my invention I propose to substitute the disk ltd, Figure id, for the disk H to thereby develop a series of trigger impulses having equally spaced periods of time.

The third disk in Figure 13, designated we, and

like the viewlshown in Figure 14, is secured to the motor shaft in such a manner that when it is rotated one half of a revolution to alter the light in the photo-cell IIII (which may be substituted for the photo-cell, Figure 8) to produce a pulse be considered in step with the positive pulses of the sine form voltage wave supplied to the power amplifier 95.

The relay 99 will not operate by separate pulse from either the rectifier 98 or photo-cell Ilil. But since the motor is two pole, the rotor may be out of step several degrees; in which case the relay would receive aiding pulses from both the rectifier 98 and the photo-cell I0! and would operate to open its contacts at 97 which would include the resistance I02 in the motor circuit momentarily in order to slow its speed sufilciently over a few revolutions to slip the rotor back in step with the supply current.

From the above description it is shown that the disk secured to the motor shaft will automatically keep in step with the current supply and that the other disk connected to the motor shaft will also generate voltage waves and pulses of current in exact phase relation and in synchronism with the received signals.

This motor generator circuit or frecuency gencrating device, Figure 13, may be used to supply and to overcome this automatically Iihave pro vided a horizontal line m3, Figure 15, which is reproduced from the permanent mark 37 at the transmitting tube Figure 1 and will occur in all picture changes and frames. From a point, just I at the left of this horizontal mark I83, a ray of light is directed by mirror I06 and suitable lenses to a photo-cell I85. This photo-cell may be used in the circuit of Figure 8 which has been previously described. The transformenwinding 58 would be inductively connectedto the'winding I98, Figure 13, which winding is connected through the control relay I M. The mark will move to the left, should the motor speed lag the picture speed which will render relay Hll inopertronbeam will be reduced just at the right in i ative and give a slightly longer interval for the horizontal lines. However, should the motor speed lead the picture time the mark would move to the right causing light to enter the photo-cell I05 which would operate relay I01 momentarily to include resistance I08 in the motor circuit, thereby reducing the speed of motor. This fea-' ture has been disclosed in my prior application, referred to before.

The mark I03, Figure 15,. also 'serves another purpose, that is, it automatically controls the, brightness of the picture reproduced by the reflections of the changes in the intensity of the line or mark I03 into the photo-cell I09 from the mirror. The photo-cell I 09 may be substituted for the one shown in Figure 8, whereby this circuit will function to adjust the bias on previous stages as shown in Figure 2 to assist in maintaining the brightness in the reproduced picture practically constant.

With reference to Figure 16, I have shownmy improved pick up tube I, which improvement. consists in dividing the metallic plate on the back of the mosaic H0 into two parts III and H2, better shown in top view Figure 17, with conductors extending from each metallic plate through the tube, the mosaic may be in two parts also, otherwise this pick up tube is of conventional design. Theconductor II3 extending from the smaller of the two plates III which is located on the left side of"'the tube facing the front, controls the grid excitation of grid H6 of amplifier tube H5.

The anode of tube H5 isconnected through primary winding 'IIS'of a transformer to positive battery.

the mosaic H0 when scanning the image it will at the end of each scanning line he focused on a vertical image of full height of. the picture caused by a narrow permanent flat bar I I1, shown outside the lens system in Figure 1. This mark will appear in all the fields, so that each time the scanning beam reaches this vertical image a small .potential change will be produced in the grid I Id of theamplifier H5, which may be further amplified in other stages to in turn produce a pulse of current in the primary transformer winding H6 which is induced into the secondary transformer winding lit to change the potential on the'vcontrol grid H9 to reduce the intensity of the electron ray during the retrace period which is commonly known as blanking. These pulses, before being applied to the control grid may be slightly delayed by well known pulse delaying methods so that the intensity of the elecstant.' 5

With reference to Figure 18, I have shown a very similar arrangement to that shown in'Figure 16 for blanking the electronray in the viewing tube at the-receiver.

The element I 20 On the inside of the viewing tube and near the right edge'facing the front, is composed of two metallic plates I2I and I22 separated by insulating material l23. From the plate I2I a lead I25 is brought out from the vacuum tube29 and extends to the grid I 25 of tube I26 which is a similar circuit to that shown and explained in connection with Figure 16, and as thej 'i' electron ray contacts the plate I22, at the end of each scanning line a potential change is produced on plate I2I for changing the potential of the control grid I21 after proper amplification and as explained for the pick up tube. Thus at the end of each horizontal line the intensit of -ment for blanking the electron ray-in pick up and viewing tubes during the vertical and horizontal line retrace. will be understood that numerous modiflcations are possible without departing from the spirit of my invention or the scope oi the claims. This application is a division of application Serial Number 334,864, filed May 13, 1940, and now Patent Number 2,320,699, issued June 1, 1943. Having thus described my invention, I claim: 1. In a television system, a cathode ray camera tube having an image plate and an electron ray directed toward the image plate, a motor, means for moving the said electron ray forward and backward horizontally and vertically to scan the said image plate, including variable speed mechanism driven by said motor, said mechanism provided with apparatus and suitable circuits forv of intercepted light beams, photo electric devices having suitable circuit arrangements actuated by the said intercepted light beams to develop impulses of current from a source of direct current in synchronism with the positive polarity pulses of the received alternating current signals, said impulses of current developed from the source of direct current for controlling the movement of the electron ray in vertical directions during spaced periods of time, and for controlling the electron ray to scan horizontal lines during each of the said periods to produce successive images from received picture signals, and means for developing intervals of longer duration in alternate vertical periods to scan even line locations on said image plate during the alternate periods and to scan odd line locations on said image plate during the intervening periods.

6. The system, in accordance with claim 5, in which there is provided switching means to vary the number of line locations that may be periods.

developing horizontal control signals, and verti- I image plate, whereby even line locations on the said image plate are scanned during alternate periods and odd line locations on said image plate are scanned during the intervening periods.

2. The system, in accordance with claim 1, in which there is provided means for changing the speed of said mechanism to thereby change the number of times that the said image plate may be scanned during a certain interval.

3. In a television system, a cathode ray viewing tube provided with an image screen and an electron ray directed toward the image screen, a mo tor arranged to be driven by received synchronizing signals, means including variable speed mechanism driven b said motor for moving the a said electron ray forward andbackward horizontally and vertically over the said image screen to produce successive images from received picture signals, said mechanism provided with ap- Daratus and suitable circuits for producing horizontal control signals, and vertical control signals having alternately short and long periods of time between signals, means actuated bysaid horizontal signals for immediately stopping the forward horizontal deflection of said ray, and means actuated by the said vertical signals for stopping the forward vertical deflection of said ray at different locations on said image screen 'to scan even line locations on said image plate during the alternate periods, and to scan odd line locations on said image plate during the intervening periods.

4. The system, in accordance with claim 3, in which there is provided means for changing the speed of said mechanism to thereby change the number of times that the said image plate may be scanned during a certain interval.

5. In a television system, a cathode ray viewing tube provided with an image screen and an electron ray directed toward the image screen,

a motor arranged to be driven by alternating current signals modulated on a carrier, rotar light valves driven by said motor to vary the intens y 7. The system, in accordance with claim 5, in which there is a mark included in said images, and means sensitive to variations in light from the mark to maintain the brightness of the reproduced images substantially constant.

' 8. The system, in accordance with claim 1, in which there is provided means including a part oi said image plate to control the intensity of the said electron ray during its backward movement.

9. In a television receiver, a cathode ray tube having an image screen and an electron ray directed toward the screen, means for deflecting the said ray forward and backward to scan lines in successive fields on said screen, means for intercepting incoming control signals, means for stopping the forward deflection of the electron ray from any location that it has reached on said screen upon the reception of any of the said signals, and means for causing the electron ray to scan lines on said screen in one fleld different than the lines scanned in the previous field under the control of said signals.

10. In a television receiver, a cathode ray viewing tube having an image screen and an electron ray directed toward the screen, means for defleeting the said ray forward and backward vertically to scan line locations in successive image frames, means for intercepting incoming control impulses, and means for starting the backward deflection of the electron ray from any location that it has reached on said screen upon the reception of any one of the said impulses, and means for causing the electron ray to scan odd and even lines in alternate and intermediate flelds respectively under .the control of said impulses.

11. In a television system, a cathode, ray tube having an image screen and an electron ray directed toward the image screen, means for defleeting the said electron ray forward and backward to scan diflerent line locations on said screen, means including apparatus and suitable circuits for developing control signals, means actuated solely by the said signals for stopping the forward deflection of said ray, and means including switches for controlling the frequency of occurrence of said signals, thereby adjusting the number of line locations that may be scanned on said image screen.

12. In a television system, a cathode ray tube ward to scan diiierent line locations on said screen, a signal generator provided with suitable circuitsfor producing control signals, means re sponsive to each of the said control signals for. immediately starting the backward deflection of said ray, and manually controlled switches for changing the frequency of occurrence of said signals, thereby adjusting the number of line 10 cations that may ce scanned on said image screen.

13. In a television transmitter, a cathode ray camera tube having a screen and an electron ray directed toward the screen, means for deflecting the electron ray forward to scan line locations in successive fields on said screen, means for pro clucing control impulses, means for deflecting the electron ray backward under the control of said impulses, means for causing the electron ray to scan lines on said screen in one field difierent from the lines scanned in the previous field under the control of said impulses, and means for changing the frequency of occurrence of said impulses to change thereby the number of deflections in a iven time.

14. In a television transmitter, a cathode ray camera tube havinga screen and an electron ray directed toward the screen, means for deflecting the said ray forward during frame periods to scan line locations in successive fields on the said screen, means for producing control impulses,

means for deflecting the electron ray backward under the control of said impulses, means for causing the electron ray to scan odd and even lines in alternate and intermediate fields respecn tively under the control of said impulses, and

rneans for changing the frequenc of occurrence of said impulses to change thereby the number of frames scanned in a given time.

15. In a television system; a cathode ray tube having an image screen and an electron ray directed toward the image screen, means for de fleeting the electron ray forward and backward to scan said screen to produce thereon images from received signals, image means for control ling the intensity of the electron ray during the forward deflections to maintainthe brightness of id. in a television system, a cathode ray tube having an image screen and an electron ray directed toward the image screen, means for del tingv the electron ray rorwarol and backward both vertically and. horizontally to scan difierent line locations on said screen to produce thereon images from received signals, means for controlling the intensity of the electron ray during the iorward deflections to maintain the brightness oi the said images substantially constant, and image means for controlling the deflecting means to adjustthe lines on said screen.

17. In a television receiver, a cathode ray tube havins a screen and an electron ray directed toward the screen, means for deflecting the electron raviortvard to scan said screen, means for producing control impulses in timed relation to received signals, meansior deflecting the electron ray backward under the control oi said impulses, and means responsive to changes in irequency of occurrence of the received signals for automatically changing-the frequency of occurrence of the said impulses to change the number of deflections in a given time.

is. A. television receiver, in accordance with claim ll in which there is provided means for adjusting said deflecting means to changethe veiocity or the-electron ray over said screen to change thereby the full forward deflection time to equal the interval between said impulses,

19. The method of producing images from recelved video signals andcontrol signals, comnrisinc picture images from said video signals during trace periods in reciprocating scanning actions, developing the received control signals to reverse the scanning actions and to cause the electron ray to scan difierent line. locations in alternate and intermediate periods, and utilizing image eiiects to maintain the brilliancy of the reproduced

Images