GB521984A - Improvements in apparatus for receiving television - Google Patents

Abstract

521,984. Television. GENERAL ELECTRIC CO., Ltd., and EDWARDS, G. W. Nov. 30, 1938, No. 34884. [Class 40 (iii)] Relate to receivers of television signals of the kind shown in Fig. 1, and consists in means for causing the frame time base to be actuated at one of the interruptions a, b, ... of the frame impulse, said means being adapted to superimpose on the synchronizing impulses during their passage to the frame time base a disturbance starting substantially simultaneously with the start of one frame impulse and ending before the next frame impulse, and such as to cause at least one pulse corresponding to an interruption to rise above a critical level above which no such pulse would rise if the said disturbance were not present. The synchronizing impulses may previously be converted into pairs of oppositely directed pulses by a resistance capacity circuit having a time constant much less than T, Fig. 1. In the apparatus shown in Fig. 6, the synchronizing impulses are separated from the picture signals in a known way by a biassed rectifier V1, the main load of which is indicated at 8. These impulses are transmitted through condensers C and resistances R to a line time-base L and a frame time-base F. Moreover, the primary 9 of a transformer is inserted between the valve VI and the point 0, and the secondary 10 between the condenser C and the valve F. The stray capacities C<SP>1</SP> of this transformer give it a time constant of the order of the duration of a frame pulse and this produces an impulse which is superimposed on the impulses transmitted by condenser C ; so that the impulses reaching the valve F are of the form shown in Fig. 5a or Fig. 5b. The frame timebase is biassed to operate at the peak a or b ... in these figures which first reaches a given level. Specifications 484,412 and 514,807 are referred to.