US2047533A - Television method - Google Patents

Description

July 14, 1936. M. VON ARDENNE 2,0475533 TELEVISION METHOD Filed Sept. 29, 1932 'J/Wen/or:

Patented July 14, 1936 UNITED STATES PATENT OFFICE TELEVISION METHOD Application September 29, 1932, Serial No. 635,406 In Germany October 6, 1931 9 Claims.

According to the well known methods of television splitting up or decomposing the picture is usually effected by scanning the picture line by line with uniform speed. At the transmitter a controlling potential is generated by a photoelectric cell. This controlling potential, varied by the light intensity of the picture, controls at the receiver the intensity of a light source. In using Braun tubes, for instance, two pairs of deflecting plates are provided, controlled by two defleeting voltages, one for scanning the image of the picture in a line direction, the other one for scanning the picture transversely to the line direction. The light intensity of the picture points during the composition is controlled by varying the intensity of cathode rays (for instance by means of cutting off parts of the cathode ray beam by a shutter). Both deflecting voltages (line changing frequency and picture changing frequency) possess suitable straight line wave form.

According to the line control method used in the present case, a constant intensity of the cathode ray is used and the line potential is varied with the light intensity of the picture. Therefore in this method the intensity of the cathode ray is not varied.

According to the line control method the scanning in a line direction does not occur with uniform speed, but may be varied spot by spot by the light intensity of the picture. At the receiver a cathode ray of constant intensity is scanning at certain places with either slow or quick speed and therefore causing bright or dark parts of the picture.

In this line control method the interval for line-scanning is not constant for each line but depends upon the mean value of the light intensity of the line. If the scanning in the picture direction (transverse to the line direction) is controlled by an oscillation of straight line wave form of constant steepness, the lines could not appear in equal distances to each other. The lines being quickly scanned (dark lines) would appear in close proximity to each other, while the lines being scanned slowly (bright lines) would appear far apart. Therefore distortion in picture transmission would occur.

This distortion of picture may be removed by using an oscillation for scanning transversely to the line direction, having not a constant steepness, but a slope varied by the mean value of the light intensity of the lines. By using such a modulation of the picture voltage by the mean value of the light intensity, the lines are equally spaced. For the purpose of maintaining the scanning periods constant, according to the invention the frequencies situated below the image frequency are withheld from the elements modulating the straight line wave form.

It is a further object of the invention to employ a filter chain for withholding the frequencies situated below the image frequency.

Fig. 1 shows a part of an arragement in order to explain the modulation of the image-and line- 0 voltages.

Fig. 2 shows a television device according to the invention using the arrangement illustrated in Fig'. 1.

Fig. 3 shows a modification of the arrangement 15 illustrated in Fig. 2.

In Fig. 1 there is shown a supply transformer 20, which furnishes the heating potentials necessary for the modulating valves I5 and I6 and the rectifier valve 2|. The winding 22 of this transformer supplies the alternating potential to be rectified, necessary for generation of the plate potential, which alternating potential, rectified, is smoothed by the system 23, which is composed of condensers and resistances. The condensers suitably possess a size of 4M5 and shall be able to bear voltages up to at least 3000 volts. The resistances suitably possess a size of 3.10 ohms. The rectified plate potential now feeds a generator for producing an oscillation of straight line wave form, comprising the condensers 26 (e. g. 0.08aF) and 21 (e. g. 0.14M) charged over the valves l5 and I6 and discharged over glow lamps 25, 24. The resistances 28, 29 (e. g. 10 ohms) and condensers 30, 3| (e. g. 2/LF) serve for obtaining a suitable screened grid potential, whereby there is rendered possible the use of cathodes which do not reveal a decided saturation (for example barium cathodes). The drop in potential at tne regulable resistances 34 and 35 smoothed by the condensers 32 and 33 (e. g. 4 F) supplies the cathode potential for the two valves I5 and I6, the grids of which are modulated by the photo-cell potential, which, if necessary, may be amplified, through the medium of condensers 36 and 31 (e. g. 2 LF). The connection systems comprising the resistances 38 (e. g. 5.10 ohms) and 39 (e. g. 5.10 --10 ohms) and the condenser 40' (e. g. 2,uF) permit of the adjustment of a suitable constant bias for the pairs of 50 deflecting plates of the Braun tube. 42 and 43 are the connections for the deflecting potentials. 44 is the connection for the photo-cell potential. A resistance 46 (e. g. 5.10 ohms) is arranged in the circuit of the grid of the first valve. In the grid circuit of the second valve I. there is included a potentiometer I! for an exact adaption of'the image control potential with respect to the line control potential. By means of the potentiometer 45 the amplitude of the modulating voltage conducted from the photocell over a connection 44 and a condenser 31 to the grid of the valve it may be regulated.

By avoiding a constant deflecting oscillation governing the frequency of the image. 1. e. by inclusion of the modulation in the image potential for producing straight line wave form, a considerable difilculty arises in the transmission of films. The time required for scanning the image (1. e. for the requisite change of image) varies in accordance with the mean intensity value of the total image. The majority of film apparatus, however, require for their operation a constant rate of movement of the film. Certainly it might be conceivable froma constructional standpoint, in the case of a film transmitter, to so control the movement of the film (which in any case is usually of an intermittent kind) by moving the Maltese cross at the moment of the discharge of the condenser of the generator for producing straight line wave form by the current or potential impulse thus released. In this manner a film transmitter would be obtained, in which the average rate movement of the films is subject to fluctuations in accordance with the mean intensities. This peculiarity would be perceptible to the eye by irregular glittering and by abnormal evolution of movements. This irregularity, however, would be particularly critical as regards the reproduction of sound films, which as well known call for a completely constant run.

According now to the present invention, these difficulties are overcome by the fact that the frequencies situated below the image frequency are precluded from the modulation of the oscillations of the generator for producing straight line wave form. In practice this may be accomplished in simple fashion by provision in the modulation network, preferably behind the photocell amplifier, of a filter-chain, which cuts off as sharply as possible the frequencies situated below the image frequency.

An arrangement of this kind is illustrated more concisely in Fig. 2. In this figure. l is the Braun tube having the pairs of deflecting plates 2 and 3, the Wehnelt cylinder 4, the cathode 5, the anode 6 and the fluorescent screen I. To avoid charges on the inner surface of the tube there is provided a special screening ring 8, which preferably is taken to earth. 9 is the network connection apparatus, which supplies heating potential, the Wehnelt cylinder potential, initial potential and plate potential. The rectangle resulting on the screen I is reproduced on the film ll through the medium of a lens system Ill. The light passing through falls on to a photo-cell II, which is situated in the input of an amplifier l3, which posseses a transmission range of approximately 24 to 300,000 periods. The amplified photocell potential is conducted to a filter chain H (impervious for frequencies which are smaller than the number of pictures per second), and after the frequencies below the image frequency have been filtered out controls the control grids of the valves l5 and I5, whereby the line or image potential for producing straight line wave form are modulated. These are produced in an apparatus of the kind illustrated in Fig. 1. ll represents a commutator, which is actuated by the film advancing means and replaces the glow lamp II of Fig. l.

The effect of excluding the low frequencies from the modulation of the straight line wave form developed by the valve l6 and the condenser 21, 5 may be seen by analyzing the modulating current into its component sine waves, and considering the effect of one of these components modulating the straight line wave form. Each half period of the sine wave produces a time variation, which 10 is annulled by the following half period and following this process up to the end of the image period it is evident that the total variation in time will be due to a fraction of an old half period of the sine wave. This variation will be small for the modulating sine waves of high frequency but will be large on those of low frequency. By excluding the low frequencies from the modulating current therefore, the variations of the image periods may be made small.

If the drop in frequency of the modulation filter in the direction of low frequencies is not very sharp, the circumstances referred to in the above necessitate an additional correcting of the image potential for the purpose of maintaining equal 25 periods of scanning a complete image. This is performed in such fashion, that fluctuations in the straight line wave form developed by the valve l6 and condensers 21 result corresponding with the fluctuations in the mean intensity of 30 the image. This correction may occur. for example, as shown in Fig. 3.

The alternating potential from the output side of the amplifier I4 is passed to the grid of the additional valve i1, provided for the purpose of 35- rectification. The alternating potentials at the grid of this valve contain both the high highfrequency components as well as the critical low components. Owing to the fact that in the anode circuit of this valve there is connected a resistance system, which is small as regards all frequencies above the image frequency, but large for all frequencies below the image frequency, it is accomplished that variation in the cathode potential and therefore the grid bias of the image- 45 tilting valve takes place only at the critical frequencies below the image frequency and compensates for the low frequency components applied to the g d.

The characteristic of this correction system as 59 compared with earlier systems proposed resides in the fact that for the correction there is employed a potential which has traversed the same frequency filters through which the actual modulation potentials have also passed. 55

This is extremely important, because if the rectifying potential were to be obtained from separate photo-cells and separate amplifiers, the cor- 'rection would cause considerable difiiculties, be-

cause the frequency-characteristic of the sender G0 amplifier would require to be simulated.

The additional valve H, which is controlled by the filtered photo-cell potential, has in its anode circuit the resistance system l8, which provides the grid potential for the image potential modu- 65 lator i6. Up to a certain degree the conditions set forth in the above are fulfilled by a resistance system which consists of the parallel cone section of a condenser and a resistance, whereby in the case of an image frequency amounting to 25 pe- 70 riods suitable values result for the condenser amounting to approximately 4 microfarads and for the resistance a preferably variable resistance from a few thousand ohms up to approximately 5,000 ohms. 75

If in this manner the average steepness of the image potential has been corrected automatically to the constant value, there is the possibility of controlling at the moment of the advance moment of the film the image potential discharge by a rotary contact 4| (see Figs. 2 and 3) in constant and in synchronous fashion.

I claim:

1. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the-lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant.

2. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, said means consisting of a filter chain being preferably situated in the output circuit of the photocell amplifier.

3. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, means for performing an additional slow modulation corresponding with the mean intensity of the image, said modulation resulting in a constancy of the scanning period of one or more images.

4. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, means for performing an additional slow modulation corresponding with the mean intensity values of the image, said modulation resulting in a constancy of the scanning period of one or more images, said additional modulation being'selected in such fashion corresponding with the ability of the amplifier to amplify low frequencies that the frequencies situated below the image frequency exert no effect on the intensity of the image.

5. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of lines, means for withholding the frequencies below the image frequency from the modulation 5 of said deflecting voltages for the purpose of maintaining the scanning periods constant, and means for producing the bias of the image potential modulator by the drop in potential occurring at a resistancesystem and controlled by the filtered and'ainplified photo-cell potential.

6. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of. the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, and means for producing the bias of the image potential modulator by the drop in potential occurring at a resistance system and controlled by.

the filtered and amplified photocell potential, said resistance system being so dimensioned that the same possesses a low resistance as compared with the frequencies situated above the image frequency, and on the other hand a high resistance as compared with those situated below the image frequencies.

7. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, and means for producing the bias of the image potential modulator by the drop in potential occurring at a resistance system and controlled by the filtered and amplified photo-cell potential, said resistance system for producing the bias of the image potential modulator consisting of the parallel connection of a condenser and a resistance.

8. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, and means for producing the bias of the image poten.. tial modulator by the drop in potential occurring at a resistance system and controlled by the filtered and amplified photo-cell potential, said resistance system for producing the bias of the image potential modulator consisting of the parallel connection of a condenser and a resist- 7 ance, said condenser possesses a capacity of 4 microfarads, and said resistance a preferably variable value of up to approximately 5000 ohms.

9. In an arrangement for transmitting optical occurrences, means for producing a line deflecting voltage and an image deflecting voltage for scanning, said line frequency being modulated by the instant intensity of said image and said image frequency being modulated by the mean intensity values of the lines for producing constant spacing of the lines, means for withholding the frequencies below the image frequency from the modulation of said deflecting voltages for the purpose of maintaining the scanning periods constant, and

means for producing the bias of the image potential modulator by the drop in potential occurring at a resistance system and controlled by the illtered and amplified photo-cell potential, said resistance system being situated in the anode circuit of a special amplifier, and being modulated by the filtered photo-cell potential.

MANFRED VON ARDENNE.

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