GB631377A - Improvements in or relating to radio receivers - Google Patents

Abstract

631,377. Television receivers. WATTON, W. L. Jan. 24, 1946, No. 2331. [Class 40 (iii)] [Also in Group XL (c)] In a television receiver, interference pulses superimposed upon the picture signals and causing the signal to go beyond the normal range of picture signals are replaced by signals which vary in accordance with the average amplitude of the picture signals. First embodiment. The received signal 3 upon which is superimposed an interference pulse is applied to the control grid of the valve 6, which is adjusted, by means of the potentiometer 10 and the D.C. insertion circuit including the diode 8, to cut off at the level of maximum picture whiteness. Thus the signal applied to the valve 12 comprises interference pulses only. The signal 3 is also applied, through a delay network 16, to the valve 17, the purpose of the delay being to allow the output of valve 12 to straddle completely the interference pulse in the output of 17 so that the interference is reduced as shown at 18. The signal 18 is applied through an integrating network to the grid of cathode-follower 25, the output of which is consequently dependent on the average amplitude of the picture signals, since the interference has been largely removed by the valve 12. The output pulses from the valve 6 are also applied to valve 19 and thence to the anodes of the diodes 21, 22, which are normally cut off. During an interference pulse, however, they become conducting so that the output from the cathode-follower 25 is' applied to the cathode-ray tube in place of the signal 18. Second embodiment, Fig. 2 (not shown). The input signal, which is in this case inverted relative to the signal 3, is applied to an amplifier which limits just above the white -level to remove the greater portion of the interference. The amplifier output is applied to (a) a further amplifier and thence to the cathode-ray tube; (b) an integrating circuit; and (c) a further limiter which selects the interference pulses from the composite signal. The selected interference pulses are combined in a diode circuit with the integrator output, which modifies the pulse amplitude in accordance with the mean signal-amplitude, the signals then being applied to the cathode-ray .tube in parallel with the further amplifier to reduce the interference pulses to the mean-picture-signal level. Specification 470,140 is referred to. Reference has been directed by the Comptroller to Specification 470,140.