GB540590A - Improvements in television receivers - Google Patents

Abstract

540,590. Television. HAZELTINE CORPORATION. June 20, 1940, No. 10624. Convention date, Feb. 7. [Classes 40 (iii) and 40 (v)] In a system in which video signals are transmitted by amplitude modulation and synchronizing signals by frequency modulation, and the line synchronizing signals are constituted by short pulses of a particular deviation from the normal carrier frequency and the field signals by longer pulses of a different deviation, as in Specification 529,320, the line and field signals are separated by tuned circuits, one being more broadly selective than the other The output from the intermediate frequency amplifier 14 passes (1) to the amplitude modulation detector 15 from which video signals pass to the cathode-ray receiver 17, (2) to the line-pulse intermediate-frequency selector 25 to control the line-scanning unit 18, and (3) to the field-pulse intermediate-frequency selector 30 to control the field-scanning unit 19. The line-pulse selector 25 is broadly tuned to the intermediate frequency corresponding to the line synchronizing signal and is connected through a rectifier and amplitude selector 26, line-frequency selector 27, and line-pulse shaper 28 to the linescanning unit 18 The unit 26 comprises a rectifier 36 and condenser-resistance combinations 37, 38, one of which has a long time constant so as to bias the rectifier 36 to prevent the passage of weak pulses representing video signals, field synchronizing pulses, &c Pulses from the linefrequency selector 27 pass to the A.V.C. rectifier 29 controlling units 12, 13, 14. The field-pulse circuits 30, 31 are similar to units 25, 26, except that the selector 30 is sharply tuned to the intermediate frequency corresponding to the field synchronizing pulse. The deviations from the normal frequency representing the line and field pulses may be in the same direction (Fig. 3, not shown) or in opposite directions (Figs. 5 and 6, not shown) and in each case the field pulses are of longer duration than the line pulses and may be arranged between two line pulses.