| 摘要 |
701,902. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 3, 1950 [Feb. 28, 1950]. No. 5107/50. Class 40 (3). [Also in Group XL(c)] In an interlaced television system, the scanning spot is oscillated at a high-frequency so as to explore, in each scan, the whole of the target electrode on which the signals are stored, and the output circuit is gated during the scan so that, although all the stored signals are wiped out, only those appropriate to the scan are passed. The arrangement is stated to eliminate distortion caused by interference with the storage of a succeeding image by those parts of the preceding image left unscanned. In the system illustrated, which is a sequential-field, line-interlaced, colour system, the scanning spot is given the normal line and field deflections by sources 2, 3 and, in addition, is given a supplementary high frequency deflection at right angles to the line direction by source 4 applied through shaping circuit 5. Preferably this oscillation is of square wave form although a satisfactory result is obtained by using a sinusoid plus the third harmonic. The frequency of the oscillation is several times picture point frequency, and the amplitude is made equal to a line width whereby during each interlaced scan the regions of the intervening lines are covered and signals from the whole of the target area are wiped off. In order, however, to take off only the signals required, the output across resistor 6 is "sampled" by a gate stage 7 opened under the control of source 4 only when the spot is traversing the line appropriate to the scan. A low-pass filter 10 eliminates the high-frequency oscillation component from the output. The invention may be applied to a dot and line interlaced system, the gate in this case being opened under joint control of the high-frequency oscillation and the dot oscillation. The invention is also of application in a radar system where a television camera operating with conventional interlaced scanning observes a P.P.I. type of display to derive signals for transmission to a remote point. Reference is made to tele-kinematograph systems. |
