| 摘要 |
799,132. Television. PHILIPS ELECTRICAL INDUSTRIES, Ltd. June 24, 1955 [June 29, 1954; Oct. 14, 1954], No. 18337/55. Class 40 (3). [Also in Group XL (c)] In an impulse noise suppressor for a television picture receiver, a band of the higher signal frequencies is selected from the I.F. spectrum on the assumption that the signals in this band are due more to interference pulses than to picture signals and such signals are separately demodulated and used either to gate the synchronizing pulse separator (in the case of negative modulation) or to " black spot " the C.R.T. (in the case of positive modulation). The whole sideband is assumed to be 5 Mc/s. wide; the frequency band selector is centred approximately 3 Mc/s. from the carrier and has little or no response to frequencies lower than those corresponding to the 20th harmonic of the line scan frequency. In one embodiment, Fig. 2, for negatively modulated signals, the output of the last I.F. amplifier 5 is passed to a detector 7, amplifier 14, and hexode 20 which passes only the positive-going synchronizing pulse (plus interference pulses). Additionally, the amplifier 5 is coupled to a tuned circuit 23 having the response above defined and to an anode-bend detector 26 which provides a gating pulse to cut off the hexode 20 on the occurrence of an interfering signal pulse. A standing bias is also applied via resistor 30 to delay the application of the gating pulses. In a modification, Fig. 3 (not shown), for positive modulation, the cathode-ray tube is conventionally cathode modulated and the output of the anode bend detector is applied to the grid to act as a " black spotter." In second embodiment, Fig. 5 (not shown), again for negative modulation, the gating signal for the synch. separator is derived by anode-bend detection of the output of a filter passing a band of frequencies between 2 Mc/s. and 4 Mc/s. from the carrier. |
