GB699795A - Improvements in or relating to television systems - Google Patents

Abstract

699,795. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 3, 1950 [March 7, 1950], No. 5788/50. Drawings to Specification. Class 40 (iii). In an interlaced scanning television receiver, the spot by means of which the picture is built up is subjected to a high-frequency wobbling deflection of an amplitude such that, in any one field, the whole picture area is explored and the line structure is blurred so that each single field has the apparent structure of a complete interlaced picture. The arrangement is stated to reduce flicker and a number of associated defects. In a conventional double line interlaced scanning system, the spot is made small, about half the normal line width, and is subjected to a high-frequency wobbling deflection in a direction transverse to the lines. The amplitude of the deflection is made approximately equal to the line spacing in a complete frame whereby each line takes on the appearance of a pair of lines and the line structure simulates that of a complete frame. Preferably the deflection is in accordance with a square wave although satisfactory results may be obtained by the use of a sinusoidal wave or a sinusoidal wave plus the third harmonic. In a double line/double dot interlaced system, the spot is subjected to a wobbling deflection transverse to the lines as above, and the line scan is effected so that a pair of dots is produced corresponding to each picture point or dot at the transmitter. Where the dot pattern is produced by superposing, a high-frequency saw-tooth wave on the line deflection, the double dots at the receiver are produced by causing the receiver high-frequency saw-tooth to have double the frequency of that at the transmitter. Alternatively, where the dot structure is produced by sampling, the receiver sampling frequency is made twice that of the transmitter. Synchronism of the dot sequence between transmitter and receiver may be controlled by the frequency difference between the sound and vision carriers. When the invention is applied as above to a double line/double dot system, each transmitting picture point or dot in any one field scan is represented by four points at the receiver and each field takes on the appearance of a complete frame.