US2227401A - Television transmission arrangement - Google Patents

Description

1940- K. SCHLESINGER 2,227,401

TELEVI S ION TRANSMI S S ION ARRANGEMENT Original Filed Nov. 10, 1956 Jnven loP Patented Dec. 31, 1940 PATENT OFFICE TELEVISION TRANSMISSION ARRANGEMENT Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc., a cor poration of New York Original application November 10, 1936, Serial No. 110,042. Divided and this application May 10, 1938, Serial No. 207,073. In Germany November 18, 1935 3 Claims.

In the case of television scanning devices, which operate by the scanning of a mosaic photoelectric screen by means of a cathode ray, there has been employed heretofore, according to publications which have become known, a mechanical device, usually a light siren, for producing the correct deflection frequencies, and synchronisation signals have been produced by the same means. A method of this kind does not produce the synchronous signals as a matter of course only when the scanning ray has reached the edge of the photo-electric screen, but the initiation of the synchronisation signal depends on the particular oscillation conditions of the siren, which is coupled more or less loosely with the movement of the ray. It is known that in the case of electrically generated synchronisation signals of this nature curvature of the image coordinates very frequently occur. Even a humming component in the mains-connected apparatus may give rise to deviations from the straight line as regards the edges of the image.

Curvatures of this kind in the co-ordinates may be fundamentally obviated in an arrangement operating with scanning discs when the scanning image point itself causes the synchronisation signal, viz., when it reaches a prescribed edge of the image. It is then immaterial whether the scanning point arrives at the edge of the image with small errors in time-too early or too late. The synchronisation signal is always initiated in such fashion that the reversing points of the synchronized received-image point are all situated on a completely straight marginal line, which in these cases is the transmitted television image of the straight edge of the transmission screen. Errors in the movement of the image point are accordingly eliminated automatically in the method of the self-synchronizing scanning point.

In the parent application Ser. No. 110,042, filed November 10, 1936 the synchronisation in the case of the ikonoscope is describe. The present invention relates to a special synchronizing device in such a case of mosaic screens scanned by an electron ray.

The invention is illustrated in the accompanying drawing which shows diagrammatically a device according to the invention.

In the drawing, the deflection of the ray pro duced by cathode l is shown to be a double electrostatic deflection. As well known, there is situated behind the mosaic screen I a signal plate 5 which is separated from the screen I by an insulating support of mica or the like (not shown). The plate 5 may be connected with the grid of an amplifying tube 5 the cathode of which like the anode 3 of the cathode ray tube requires to be earthed. The illuminated points of the screen have been charged positively during the storing period and upon the scanning, supply negative impulses to the input grid of the amplifier 6. There are required for synchronisation purposes, dependent on the method of transmis sion, negative or positive impulses of considerable intensity. According to the invention, there is employed for the automatic generation of impulses of this nature when the edge of the image has been reached a special marginal electrode Ia, lb. This is a continuous conductive structure which is disposed about two edges of the image in a width corresponding to the desired duration of impulse. This synchronisation electrode I is conducted separately outside the tube and is earthed via a leakage resistance 8 and a battery 9 blessing the electrode 1 as desired in respect of extent and polarity. If the resistance 8 is large as compared with the internal resistance of the scanning system defined by the oathode ray, there are obtained by way of the common insulating plate negative synchronisation impulses when the bias 9 is applied with its positive pole to 'l and positive impulses when the bias of I is selected to be negative in relation to earth. The intensity of the impulses depends on the voltage of the bias 9. The occurrence of the signals produces in the receiver an image having straight edges when the edges of the synchronisation angle on the image side are also straight. If the scanning ray is subject to errors in time upon its scanning movement, the received image in the case of this method of synchronisation will nevertheless retain its linear form on the side directed towards the synchronisation angle.

In the practical embodiment the synchronisation electrode 1 will preferably consist of a fine silver deposit on the mica plate supporting the mosaic 5, and by methods known per se will be maintained free of photo-electric sensitivity upon the sensitization of. the intercepting plate. A slight photo activity of I will, however, not be detrimental as it may be overcome by adjusting the bias 9.

I claim:

1. A television transmission arrangement including a cathode ray tube having at least cathode, anode and two pairs of deflecting plates for deflecting the cathode ray in said tube, a photoelectric screen comprising a plurality of photoelectric cells, a metallic marginal electrode, and

an electronic amplifier, said marginal electrode being adjacent said photo-electric screen, a D. 0. potential source, means for applying a constant adjustable bias to said marginal electrode from said D. C. potential source, said photocells and said marginal electrode being connected to the input of said electronic amplifier as to produce image currents and synchronisation signals when scanning said photo-electric screen and said marginal electrode by said cathode ray.

2. A television transmission arrangement including a cathode ray tube having at least cathode, anode and two pairs of deflecting plates for deflecting the cathode ray in said tube, a photoelectric screen comprising a plurality of photoelectric cells, a metallic marginal electrode, and an electronic amplifier said marginal electrode adjacent said photo-electric screen having the same counter-electrode as said photo-electric screen, a D. C. potential source, means for applying a constant adjustable bias to said marginal electrode from said D. C. potential source, said counter electrode being connected to the input of said electronic amplifier as to produce image currents and synchronisation signals when scanning said photo-electric screen and said marginal electrode by said cathode ray.

3. In a television transmission arrangement including a cathode ray tube comprising an insulating plate. a mosaic of mutually insulated light sensitive particles on one side or said insulating plate, a signal plate on the other side of said insulating plate, means for producing a cathode beam, means for applying to said cathode beam periodic deflections in two coordinates at different frequencies to cause the beam to scan said mosaic, and an amplifying device having its input coupled to said signal plate: means for producing synchronizing impulses in the input circuit of said amplifying device, the last mentioned means consisting of a marginal electrode, mounted on said insulating plate at the same side thereof on which said mosaic is disposed, to be hit by the cathode beam in its positions of extreme deflection in one direction of any of the two coordinates of deflection so that a synchronizing impulse is capacitatively conveyed to said signal plate each time said cathode beam reaches a position of extreme deflection in one direction of one of the two coordinates of deflection.

KURT SCHLESIN GER.

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