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0a. 18, 1938. ‘c, o. BROWNE ' ' 2,133,422 TELEVISION AND THE LIKE SYSTEM Filed Feb. 14, 1934 .?'y.1 114g. 5 W z INVENTOR CECIL o. B WNE BYI7KZML ATTODNITV 2,133,422 Patented Oct. 18, 1938 ' UNITED STATES PATENT OFFICE 2,133,422 TELEVISION AND THE LIKE SYSTEM Cecil Oswald Browne, West Acton, London, Eng land, assignor to Electric and Musical Indus tries Limited, Hayes, England, a company of Great Britain Application February 14, 1934, Serial No. 711,083 ' In Great Britain February 15, 1933 (Cl. 178--69.5) The scanning of the motion picture ?lm (which The present invention relates to television and 12 Claims. is not illustrated) may be carried out in any of the like systems. It is well known in television, picture transmis i) sion and the like, to scan the object to be trans mitted in a series of parallel lines and to arrange that there occurs, between the scanning of suc cessive lines, a short interval during which syn chronizing signals are transmitted. Thus the transmitted signals comprise trains of picture '10 signals separated by synchronizing signals. The synchronizing signals are utilized at the receiver to maintain a scanning device in syn chronism with that at the trasmitter. It has been found that a difficulty arises in 15 certain systems of this kind, in that the syn chronizing signals tend to be delayed in relation to the picture signals and the synchronizing sig nals may therefore arrive at the receiver scan ning device during the reproduction of the pic .20 ture signals instead of in intervals between the picture signals. To avoid this it has been nec essary either to increase the interval between the scanning of successive lines or else to mask o? a part of the reproduced picture. It is an object of the present invention to re 25 move or reduce this difficulty. It is a further object of the present invention to provide a method of transmitting and receiv ing images of objects wherein there are gener 30 ated at a transmitter synchronizing signals and trains of picture signals having intervals between successive trains, each synchronizing signal be ing transmitted simultaneously with a train of picture signals and means being provided in the 35 transmission channel for delaying or advancing the synchronizing signals relative to the picture signals. ' - The invention will now be described,‘ by way of example, as applied to a ?lm television system, 40 reference being made to the accompanying draw ing in which Fig. 1 shows .the wave form of signals trans-1 mitted in a known form of television system, Fig. 2 shows the wave form. of signals trans mitted in accordance with one form of the pres ent invention, Fig. 3 illustrates, in greater detail, a portion of the curve shown in Fig. 2, ’ ‘Fig. 4 is a circuit diagram of television trans 50 mitting apparatus arranged and adapted to op erate in accordance with the present invention, and Fig. 5 is a circuit diagramof television receiv ing apparatus adapted to receive the signals 55 transmitted by means of the apparatus of Fig. 4, .the known ways, but preferably the ?lm is moved vertically downward at a uniform speed past a horizontal illuminated slit. An image of the 'strip of the ?lm at any instant illuminated is swept, by one of a number of mirrors carried on a rotating mirror drum, over an apertured photo-electric cell, thereby scanning this strip or line and generating in the cell picture signals 10 corresponding to the light and shade of the line scanned. The drum is rotated about a vertical axis and all the mirrors lie in planes parallel to this axis. The arrangement is such that, after one mirror has swept its image over the cell ap 15 erture, a short interval occurs before the next mirror commences to sweep an image over the cell. In this manner there are generated in the photo-cell a series of trains of picture signals of 20 the kind illustrated in Fig. 1. During the scanning of each strip of the ?lm, the mirror which is performing the scanning function also sweeps an image of a second il luminated slit over a second apertured photo 25 electric cell thereby generating in this cell an electrical pulse known as a line pulse. The dura tion of this line pulse is made approximately equal to or less than the interval between suc cessive trains of picture signals, that is to say, 30 less than the interval l shown in Fig. 1. In a manner which will be described later each line synchronizing pulse is converted into a symmetrical train of pulses and superimposed upon the picture signals as shown in Figs. 2 35 and 3. ‘ When one complete frame of the ?lm has been scanned in this way, a rotating shutter becomes operative to intercept thev light from the two slits above referred to for a time about equal to 40 that required for the scanning. of ?ve lines. Slightly before this time, during the scanning of the ?lm image, a member rotating with the shut ter uncovers a third illuminated aperture 01‘ slit and allows light therefrom to fall upon a third 45 photo-electric cell generating in this cell what is called a frame synchronizing pulse. The du ration of the frame pulse is made approximately ‘equal toy or less than the time during which the shutter is operative. ~ 50 Both the line and frame pulses are converted in any convenient way, one of which will be de scribed later, into trains of oscillations at a sub carrier frequency, ‘that is to say at a frequency lower than that of the carrier on which the trans 55 2 2,133,422 I mission is to be effected and‘ higher than the highest frequency of importance in the picture signals. The duration of these trains are equal to the durations of the line and frame pulses respectively from which they are derived. Referring now to Fig. 4, the trains of picture 26 from valve I2 consist of symmetrical trains of sub-carrier frequency. ' In a similar manner the frame pulses applied to the transformer 6 operate to raise the poten tial of the grid of valve 2| above its normal neg ative value so that current ?ows in the anode signals, of the wave form illustrated in Fig. 1, circuit, whilst the sub-carrier oscillations ap are ampli?ed in the thermionic valve 2, the pulses plied to transformer 8 have the effectof chop generated at the line frequency are applied, as ping this current at sub-carrier frequency. The 10 indicated by the arrow 3, across the primary frame pulse components are not removed, how winding of the transformer 4 and the longer ' ever, since they serve a useful purpose at the pulses generated at the frame frequency are ap receiver which will be described later. plied, as indicated by the arrow 5, to the pri The parallel tuned circuit I4 is tuned to th mary winding of the transformer 6. An oscillator sub-carrier frequency and is designed to have a 15 of any known or suitable hind, adapted to oscil high impedance at this frequency relative to 15 late at the sub-carrier frequency is connected, that of the circuit 21 and resistance I5 so that as indicated by the arrow ‘I, across the primary all components of sub-carrier frequency are re winding of the transformer 8. moved from the picture signals. The output of The secondary winding of the transformer 4 is valve 26 for about three lines of the picture connec‘ ed across a potentiometer resistance 3, a scanned is thus somewhat as shown in Figs. 2 20 suitable portion of this resistance, that between and 3. ‘ the sliding contact I0 and the point I I, being con The arrangement may also be considered in the following light. nected in the grid-?lament circuit of a ther mionic valve I2. The anode of valve I2 is com I The valve 2 operates as a generator connected 25 nec‘ed, through resistance I3, the parallel tuned circuit I4 and resistance I5, to the positive ter minal of a source of current (not shown) the negative terminal of this source being earthed. Grid bias for the valve I2 is supplied by the 30 across a ?rst impedance I5 and either of valves 25 I2 or 2| operates as a generator connected across impedances I4 and I5 in series, whilst an imped ance 21 is connected in shunt with impedances I4 and I5. Because at the sub-carrier frequency, the impedance I4 is high compared to that of 30 shunt with the anode-?lament path of the valve ' either of impedances I5 and 21, the trains of sub carrier frequency supplied to the grid of valve I2 is a condenser I8 in series with an induct battery I6 shunted by the condenser II. In ance I9. The (secondary winding of the transformer 6 26 by valve I2 or 2I are ampli?ed and the com ponents of sub-carrier frequency in the picture 35 is connected across a potentiometer resistance 2|] a suitable portion of which is connected in the signal are removed. Referring now to Fig. 5, which illustrates ap grid-?lament circuit of a thermionic valve 2|. The anode of valve 2| is connected through cir cuit I4 and resistance I5 to the positive side of a 40 source of current and grid bias for valve 2| is supplied by battery 22 in shunt with which is a condenser 23. The filaments of the valves I2 and 2| are paratus adapted to receive the signals trans earthed as also is one end of the secondary wind 45 ing of transformer 3, the other end of this wind ing being connected to points II and 24, so that the secondary winding of transformer 8 is con nected in the grid-?lament circuits of both of valves I2 and 2|. The anode of valve 2| is connected through 50 35 mitted with the aid of the apparatus of Fig. 3 and to reconstitute images of the transmitted pictures upon a cathode ray tube, the composite 40 signal is applied, after detection and, if neces sary, ampli?cation, to the grid-?lament circuit of a thermionic valve 30. The anode of the valve 30 is connected, through a resistance 3| to the positive terminal of a source of current (not 45 shown) and the ?lament is earthed. In par allel with the anode-?lament path of the valve are connected in series, a condenser 32, a par allel tuned circuit 33 tuned to the sub-carrier frequency and circuit 34 consisting of a con 50 condenser 25 to the grid of a third thermionic denser and resistance in parallel. The cathode of the cathode ray tube (not valve 26, the output of which forms the com shown) is earthed and the grid or modulator mencement of the transmission channel. Cir cuit 21 comprises a grid leak 28 for valve 26, and ’ electrode of the tube is connected to a point 35 between .the circuits 33 and 34. The circuits 33 55 a condenser 29 shown in dotted lines which rep and 34 form two arms of a bridge, the other two resents the'stray capacity of valve 26. The operation of the arrangement is as fol— arms of which are constituted by a resistance 36 and a parallel tuned circuit 31 tuned to the sub lows: The valves I2 and 2| are biased negatively to carrier frequency. The impedances of circuits 33 and 31, at the 60 such an extent that in the absence of line and sub-carrier frequency, are high compared to frame synchronizing pulses respectively, no cur those of the resistance 36 and circuit 31 so that rents flow in these valves. When a line synchro nizing pulse is applied to the "primary winding of transformer 4 the potential of the grid of valve 65 I2 is raised ‘positively with respect to the ?la ment until current ?ows in the anode circuit; on account of the oscillations of sub-carrier fre quency applied to transformer 8, however, a train of signals of sub-carrier frequency ?ows 70 in the anode circuit of valveuI2, the duration of this train being equal to the duration of a line‘ synchronizing pulse. The shunt circuit I8, I3 is designed to by-pass the line pulse frequency with about vits ?rst ten harmonics so that the line 75 synchronizing signals supplied to the grid of valve the component of sub-carrier frequency is sub stantially eliminated from the signals developed across the circuit 34 which are applied to the cath 65 ode ray tube. These signals thus consist of trains of picture signals together with pulses at the frame frequency. The delay of the sub-carrier signals relative to the picture signals (produced by the circuits tuned to the sub-carrier frequency) is of the order. of a few micro seconds and whilst this is suf?cient to bring the line synchronizing signals into the intervals between trains of picture signals, has relatively little effect upon the position of the 3 2,183,422 frame signals relative to the trains of picture‘ signals. successive trains comprising transmitting simul taneously the synchronizing signals witha train The pulses of frame frequency which were re tained in the transmitted signals may therefore be used to “black out” the picture in between of video signals, forming each synchronizing sig- . nal from a train of signals of a sub-carrier fre frames. quency, and delaying or advancing the synchro nizing signals in time relationship relative to the , video signals in the transmission channel. - Alternatively the pulses of frame frequency may be removed from transmitted signals and the 2. The method claimed in the preceding claim comprising in addition the step of removing from timing of the generation of frame pulses at the 10 transmitter be so chosen that thegframe syn the video signals that component thereof which is 10 chronizing signals of sub-carrier frequency occur, at the receiver, in the intervals between pictures. Since the impedance of resistance 36, at the sub-carrier frequency is low compared to that of 15 the circuit 31, the trains of synchronizing signals of sub-carrier frequency are selected from the composite signal and passed on to the grid of valve 38 where they are ampli?ed before being detected, separated and applied to their appro of the sub-carrier frequency. 3. The method of transmitting and receiving images of objects wherein there are generated at a transmitting station both synchronizing sig nals and trains of video signals having time 15 intervals between successive trains which in cludes the steps of producing synchronizing sig nals in the form of a train of signals of a sub carrier frequency, producing video signals, lim iting the time durationof the synchronizing sig 20 priate synchronizing units (not shown). nals to a period at least no greater than the dur ation of the intervals of time between successive trains of the video signals, removing from the video signals that component thereof which cor responds to the sub-carrier frequency, and con» 25 It is in the synchronizing units that the major portion of the delay of the frame and line syn chronizing signals relative to the picture signals occurs. 25 Each set of synchronizing signals is used in trolling in the receiver the delay or advance in any known or suitable manner to control the gen eration of a saw tooth wave, one of these waves time of occurrence of the synchronizing signals relative to the video signals in order to place the serving to control the de?ection of the cathode ray in one co-ordinate and the other to control synchronizing signals in the time intervals be 30 tween successive trains of video signals. 4. In television apparatus wherein video and synchronizing signals are transmitted upon a 30 the de?ection in the other co-ordinate. ’ If the moment at which the line signals are gen erated at the transmitter in relation to the pic ture signals has beenv correctly chosen, the return strokes of the line scanning movements will occur 35 in the intervals between the reproduction of suc cessive lines. In Fig. 6 there is shown a receiver circuit ar rangement somewhat similar to that shown in Fig. 5, like parts in the two ?gures being given like reference numbers. In the case of Fig. 6 how single carrier frequency, means for producing the synchronizing signals in the form of a wave train of energy of a sub-carrier frequency, 35 means for removing from the video signals that component thereof which is of the sub-carrier frequency, means for superimposing the syn chronizing signals upon the video signals during a scanning of an elemental strip of the object 40 ‘ ever, the parallel tuned circuit 33, which serves to . of which the electro-optical representation is to eliminate the component of sub-carrier frequency be produced, and means for controlling the time from the picture signals also serves to select the period at which the produced synchronizing sig nals are effective in the receiver to cause the sub-carrier signals and pass them on to the am 45 plifying valve Bil. _ synchronizing signals to appear in the time in 45 tervals between successive trains of video signal ' The present invention is also applicable where the picture signals are delayed more than the energy. synchronizing signals, the synchronizing signals in _ - this case being generated and transmitted later 50 than if the delay did not take place. The invention as set forth above will be seen to provide means for in effect, advancing or re 5. The system claimed in the preceding claim wherein the time control system for controlling the synchronizing signals in time of occurrence 50 comprises a first and. second impedance connect I, ed in series, a thermionic valve, and a third im tarding the synchronizing signals in relation to pedance in parallel with said ?rst and second the picture signals to compensate for delay oc ' impedances and connected across the output of said thermionic valve, means for applying the 55 55 curring at another part of the system. ‘ In some forms of television and the like systems, synchronizing signals are generated at the trans mitter and are used to control the scanning both at the transmitter and at the receiver. An exam 60 ple of such a system is one using a cathode ray video signals across the first named impedance and means for applying the synchronizing sig nals across the ?rst and second impedance, the said second impedance being of high value com pared to that of the ?rst impedance measured 60 at radio frequency and said-second impedance tube for generating the picture signals at the transmitter. In applying the present invention ' being in the form of a tuned circuit tuned to the to such a system, where the synchronizing sig sub-carrier frequency. nals are delayed in transmission more than the 6. Means for receiving television signals in the 65 picture signals or vice versa, means are provided either at the transmitter or at the receiver for suitably advancing or retarding the synchronizing signals relatively to the picture signals so that the delay introduced in transmission is com 70 pensated. I claim: form of a wave train of energy representing video 65 signals having intervals between successive trains and synchronizing signals in the form of trains of oscillations of a radio frequency super imposed upon the video signals and wherein each interval between successive trains of the video 1. A method of transmitting and receiving im signals is at least equal to the duration of one ages of objects wherein there are generated at of the trains of radio frequency oscillations com prising means for receiving the modulated car rier, means for separating from the received car the transmitter station synchronizing signals and 75 trains of video signals having intervals between 75 4 2,133,422 rier modulation oscillations of a sub-carrier fre nizing signals superimposed upon said picture quency, a pair of series connected circuits where signals. ' in one of said circuits is of high impedance rela ‘ tive to the second at the sub-carrier frequency, 10. Apparatus according to claim 9 wherein means are provided for generating said radio whereby synchronizing signals are controlled as frequency signals during the scanning of a strip to time in order to delay or advance the effective ness thereof to time periods separating successive of said object. 11. Apparatus for transmitting images of objects in the form of trains of picture signals having intervals between successive trains and synchronizing signals in the form or trains of 10 trains of the video signals. , 7. A method of transmitting and receiving 10 images of objects wherein there are generated at a transmitter synchronizing signals and trains of picture signals having intervals between the successive trains comprising the steps of gener ating synchronizing signals and picture signals 15 simultaneously, and delaying or advancing the synchronizing signals relative to the picture sig nals prior to the transmission of said signals. 8. A method in accordance with claim '7 where in there are generated synchronizing signals oi 20 duration substantially equal to the duration of one of the intervals between successive trains of picture signals. 9. Apparatus for transmitting images of objects in the form of trains of picture signals having oscillation of a radio frequency comprising means for generating picture signals, means for gen erating synchronizing signals of a radio fre quency simultaneously with the generation of said picture signals, means for compensating for 15 advancing or delaying of said synchronizing sig nals relative to the picture signals at a receiver comprising ?rst and second impedances con nected in series, a third impedance connected in parallel therewith, a thermionic valve having 20 anode, cathode, and control electrodes, said con trol electrodes being connected to said third impedance, means for applying picture signals of a radio frequency comprising means for gen across the ?rst impedance, means for applying synchronizing signals across the ?rst and second impedances, and means for transmitting said ad vanced or delayed synchronizing signals super erating picture signals, means for generating imposed upon said picture signals. intervals between successive trains and synchro nizing signals in the form of trains of oscillation synchronizing signals of a radio frequency simul 30 taneously with the generation of said picture sig nals, means for compensating for advancing or delaying of. said synchronizing signals relative to the picture signals at a receiver, and means for transmitting said advanced or delayed synchro 12. A method in accordance with claim 7 wherein there are generated synchronizing sig 30 nals of a radio frequency of_ a duration less than the duration of one of the intervals between suc cessive trains of picture signals. CECIL OSWALD BROWNE.