GB690108A - Improvements relating to television receivers - Google Patents

Abstract

690,108. Television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Feb. 23, 1951 [Feb. 23, 1950; April 29, 1950], Nos. 4615/50 and 10588/50. Class 40 (iii). In a television receiver, the line structure is rendered less noticeable by applying the output of an oscillator operating at a frequency much greater than line frequency to the cathode-ray tube to reduce the intensity of the beam and cause each line of the image to be formed as a series of spaced dots, the oscillator being synchronized by the line synchronizing signals. The amplitude of the oscillations may be varied automatically in accordance with the brightness of the image. Fig. 3 shows a receiver operating with interlaced scanning. An oscillator 8 having a frequency of, for example, 2.7 Mc. is synchronized from the line synchronizing pulses 9, and oppositely-phased outputs 12, 13 obtained from the secondary of transformer 11 are applied through gate stages 16, 17 to a transformer 19 connected with an intensity-controlling electrode of the cathoderay tube (not shown). The gates are rendered effective alternately during successive frames by square-wave signals 24, 25 from multi-vibrator 22 synchronized by the frame synchronizing pulses 23. Fig. 4 shows the dot structure produced on the cathode-ray tube screen, the dots of alternate lines being staggered since the oscillations producing them are displaced in time by half a period. Fig. 1 (not shown) illustrates a receiver employing an oscillator with a single output to produce a dot structure in which the dots of successive horizontal lines are disposed in vertical columns. U.S.A Specification 2,479,880 is referred to.