Patent GB-926798-A (GB)
Title: Improvements in or relating to television systems
Inventor: DAVIES ERIC
IPC: H04N3/34
Filed: 1960-10-26
Abstract: 926,798. Television. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. April 6, 1961 [Oct. 26, 1960], No. 36743/60. Class 40 (3). In a television system a 50% reduction in bandwidth requirement is effected by transmitting signals representative of spaced picture elements in each line as shown in Fig. 2 for a sequential system and in Figs. 3 and 4 for a (double) interlaced system and, at the receiver, deriving from successively received signal elements further signal elements which are utilized to reproduce picture information in the spaces between the picture elements reproduced directly from the received signals. At the transmitter (Fig. 1, not shown) the signals are produced by applying a (e.g. rectangular) spotwobble (Figs. 2 to 4) to the beam of the pick-up tube (that shown in Fig. 3 being staggered for clarity) a synchronising component of which is transmitted for utilization at the receiver. In one form of receiver (Fig. 5) the separated picture signals are fed directly over line 14 to a first reproducing tube T1 and via a valve 17 and through a one-picture-element period delay line 18 and a valve 16 to a second reproducing tube T2, the valves 16, 17 each being adjusted to deliver an output of one half the amplitude of the signals on line 14 and both tubes being scanned by generator 20 (controlled by synchronising signals on line 12) with the spot-wobble scanning of tube T2 phase displaced by 180 degrees with respect to that at the transmitter (and that at T1). The two reproduced pictures are then optically combined. In a modification of this arrangement a third valve is connected in parallel with the valves 16, 17 and supplied with picture signals delayed by two picture-element periods. Each valve is arranged to produce an output equal to one third the amplitude of the signals fed to tube T1 and to compensate for the additional delay in the signals fed to tube T2 a delay equal to one picture element period is introduced into the signal fed to tube T2 (Fig. 6, not shown). The latter delay may be dispensed with and compensation effected by optically superimposing the two images with a relative displacement, in the line direction, equal to one picture element. Instead of employing two separate reproducing tubes a single two-gun (or a split-gun) tube may be employed (Fig. 7, not shown). Fig. 8 shows the type of reproduction obtained with sequential line scanning (from Fig. 2 transmission) with the spot-wobble frequency equal to an octal harmonic of one half the field frequency and Figs. 9A and 9B the interlaced case (from the transmissions of Figs. 3 and 4 respectively) if the spot-wobble frequency is equal to an odd harmonic of one quarter the field frequency. The hatched circles represent the picture elements due to actual received picture signals and the unhatched circles represent " re-constituted " picture elements, and both sets of circles interchange, after each sequential field in the case of Fig. 8, and after every two fields, in the case of Figs. 9A or 9B. In a modification employing one single beam picture tube (Fig. 11, not shown) an additional relatively highfrequency wobble (Fig. 10, upper waveform) deflecting the beam between two successive lines is superimposed on the rectangular wobble (Fig. 10, centre waveform) and the picture signal input to the tube is controlled by a switch operating at the high-frequency wobble rate and supplied with picture signals (e.g. from the lines 14, 19 of Fig. 5) in a change-over switch operating at the rectangular wobble frequency thus producing a dot display as shown in the lower portion of Fig. 10.