GB545756A - Video-frequency signal-translating system for television receivers - Google Patents

Abstract

545,756. Television. HAZELTINE CORPORATION. June 30, 1941, No. 8225. Convention date, July 23, 1940. [Class 40 (iii)] Retrace lines are extinguished in cathode-ray tube television receivers by means of a circuit which isolates synchronizing pulses, integrates the field pulses and feeds the integrated voltage into the image circuit to vary the signal level corresponding to black applied to the cathode-ray tube. In the form shown in Fig. 1, the detected signal is supplied to the cathode-ray tube 17 through a diode 22 which stabilizes the black-level and a tapping on the diode load resistance 26 is connected to a rectifier 35, which isolates the synchronizing pulses for controlling the synchronizing signal separator 19 connected to the line and field scanning circuits 18. In addition, the field synchronizing pulses are integrated by the resistance 33 and condenser 34 ; and the integrated voltage is fed by condenser 32 to the cathode-ray tube to vary the black-level of the signal to suppress the ray during a substantial part of the field retrace period. In a modification, Fig. 3, the detected signal is supplied from the detector 15 to the cathode-ray tube 17 through two amplifier stages 22, 39, the first one of which has a diode 37 in its grid circuit to stabilize the black-level, and a tapping on its load resistance 26 connected to a diode 43 with a load resistance 44 for isolating the synchronizing pulses, and a resistance 45 in series with a condenser 46 for integrating the field pulses. The voltages on the resistance 44 and on the condenser 46 control electrodes of a repeater tube 47, the output of which controls the synchronizing signal generator 19 for the line and field scanning circuit 18, and also controls through a condenser 51 an electrode of the second amplifier 39 to vary the black level of the signal fed to the cathode-ray tube 17.