GB850024A - Improvements in or relating to television systems - Google Patents

Abstract

850,024. Television. SYLVANIA-THORN COLOUR TELEVISION LABORATORIES Ltd. Jan. 9, 1959 [Dec. 2, 1957], No. 37537/57. Class 40(3). In a television receiver the scanning spot is deflected in a direction perpendicular to the lines by an oscillation of a frequency much higher than the line frequency, the oscillation being locked to the line frequency and the amplitude being so chosen that the crests and troughs of the resulting undulatory lines are collinear or approximately collinear with and interlaced with, either the crests and troughs respectively of the same line in the immediately preceding field, where simple line sequential scanning is employed, or respectively the troughs of one and the crests of the other of two adjacent lines of the immediately preceding field where interlaced scanning is employed. Fig. 2 illustrates the invention as applied to interlaced line scanning the high frequency oscillation being made an integral multiple of line frequency, and Fig. 3, illustrates the invention as applied to line sequential scanning, the oscillation being made an integral multiple of line frequency plus half a cycle, or generally an odd multiple of half picture frequency. Fig. 4 (not shown) illustrates a particular case of line sequential scanning where the oscillation is made equal to an odd multiple of half the line frequency and the number lines is odd. A general effect of the invention is to lay down a pattern of dots defining a diamond matrix with the dots in one field occurring at the centres of the diamond in the next field. The oscillation may comprise a sine wave, with added harmonics if desired, a square wave or a triangular wave. Reference is also made to the use of a sine wave with a second sine wave oscillation of twice the frequency applied in the line scanning direction. The frequency of the oscillation is selected to be between 1À3and 1À7 times the maximum video frequency, a preferred value being about 1À4 times. Reference is made to a frequency chosen so that the diagonals of the diamond matrix are at right angles. Figs. 5 and 6 (not shown) illustrate the application of the invention to a colour television receiver utilizing a repeating sequence colour line display with the lines arranged horizontally. Figs 7 and 8 (not shown) illustrate a similar application where the lines are arranged vertically. The oscillation is locked to the colour sequence by means of either a received colour synchronizing signal (e.g. the N.T.S.C. synchronizing "burst"), or an indexing signal generated in the receiver. Preferably the transmitter is scanned in the same manner as the receiver, the receiver oscillation being maintained in phase with that transmitter either by deriving it directly from the line synchronizing pulses or by means of a synchronizing signal sent from the transmitter. In this respect Fig. 9 (not shown) illustrates various possible frequency allocations for a system according to the invention as applied to both monochrome and colour transmission based on the N.T.S.C. system. The transmission includes a sound signal and reference is made to the use of the sound carrier for synchronizing the oscillation.