GB886086A - Apparatus for controlling television signals - Google Patents

Abstract

886,086. Television. FERNSEH G.m.b.H. Nov. 5, 1959 [Nov. 5, 1958], No. 37636/59. Drawings to Specification. Class 40(3). Relates to apparatus for controlling television signals comprising means for applying television signals from each of two television scanners to a combining circuit by way of gate circuits which are opened alternately by the action of a keying signal produced by scanning a master pattern by means of a third television scanner. The signal from the combining circuit represents a composite image in which the scene viewed by the first of two scanners is replaced by the scene viewed by the second of the two scanners over an area determined by the master pattern scanned by the third scanner. In the apparatus, means are' provided for varying the phase and/or duration of the keying signal relative to the gated television signals, in order to permit the position and/or size of the area to be adjusted, by changing the position or size of the scanning raster in the third scanner. The relative, size of the horizontal and vertical scans is also made adjustable to permit the aspect ratio of the area to be adjusted. When the scan amplitudes are increased above normal so as to overscan the area of the target in a pick-up tube employed as the third scanner, there is a tendency for the scanner to develop spurious signals. In accordance with' the invention these : are eliminated by a blanking system, Fig. 5 (not shown), which generates line and frame frequency pulses coincident with the scanning of the target and functions either to blank the tube beam except when it is traversing the target or to suppress the tube output signal except when the target is scanned. As an alternative the pickup tube may incorporate a frame electrode surrounding the target which engages the beam whenever it overscans the target and is held at a suitable potential to prevent the production of spurious signals. As an alternative to varying the area size by variation of raster size, the size of the image of the master pattern presented to the third scanner may be varied either by varying the distance of the pattern from the scanner or by use of a lens system of variable magnification. Reference is made to the rotation of the area, this being brought about either by rotating the pattern in a plane perpendicular to the optical axis of the third scanner, or by the use in the scanner of a pick-up tube including an image section in which the electron image may be rotated. Preferably a number of different master patterns may' be provided which may be carried by suitable members to permit their introduction into the optical path of the third scanner' when required. Provision is made to introduce reference level pulses into the keying signal during the blanking intervals which function to set the trigger level of a phasesplitting stage which provides oppositely phased versions of the keying signal for control of the gate circuits in the signal paths from the first and second scanners.