Patent GB-562113-A (GB)
Title: Improvements in colour television systems
IPC: H04N9/44
Filed: 1943-03-06
Abstract: 562,113. Colour te'evision; synchronizing. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. March 6, 1943, No. 3672. Convention date, June 28, 1941. [Class 40 (iii)] A colour television apparatus comprises a plurality of colour selective means repeatedly operative in a given colour sequence and phased by " colourphasing " signals, means causing the plurality of colour selecting means to operate in fixed phase relationship with respect to the " colour-phasing " signals but not necessarily in correct colour phase, means for generating " colourindicating " signals at times when the plurality of colour selecting means is in a predetermined position, and means responsive to the time relationship of the " colour-phasing " and " colourindicating " signals for causing the colour selective means to assume automatically the correct colour phase. In the apparatus shown, double interlaced scanning is used in conjunction with three successive colours. The three colours are selected in sequence by a colour wheel 16, Fig. 1, in the optical path between a scene 13 and an Iconoscope 10. The colour wheel is driven by a synchronous motor 31 locked-in with a synchronizing signal generator 17 by a lock-in circuit 62. The generator 17 may be as described in Specification 537,375. The synchronizing signal from the generator 17 controls the scanning operation of the Iconoscope 10 through the line 18 and the circuits 19, 21, 22, the production by a circuit 33 of a " colour-phasing " pulse 34 at every third frame and the production by a circuit 37 of a high frequency of 500 kc. A circuit 36 fed from the circuits 17, 33 serves to blank out at every third frame three of the narrow pulses 46, Fig. 4, of the frame pulses produced by the generator 17 ; a circuit 38 fed from the circuits 33, 37 serves to produce in place of the three blanked out pulses three trains 47, each comprising oscillations at the 500 kc. frequency generated by the circuit 37. The outputs of the circuits 36, 38 are combined and fed to the transmitter circuit 26, which also receives the image signal from the Iconoscope 10 through amplifiers 23, 24. The colour wheel 16 comprises two sets of three colours as shown in Fig. 2, and is formed with diametrically opposite notches 50, which produce pulses in a pick-up coil 51. These pulses constitute " colour-indicating signals and are fed through a transformer 52 to the grid of an amplifier tube 27, the anode of which is fed through a transformer 53 with the " colour-phasing " signal 34 generated by the circuit 33. The anode of tube 27 is connected to a rectifier 25 followed by a D.C. amplifier 30. The tube 27 is so biassed and its circuit so designed that when the " colour-indicating " and the " colour-phasing. " pulses coincide, the amplifier 30 passes no current through a solenoid 28, and the colour wheel remains clutched to the motor 31. If these pulses do not coincide, the tube 30 passes current, the solenoid 28 deflects a lever 56 and a clutch 29 allows the colour wheel 16 to slip relatively to the motor 31, whereby the colour wheel and the synchronizing signals are brought into correct colour phase. The circuits at the receiver operate in a similar manner, a pulse equivalent to the pulse 34 being extracted from the pulse trains 47 of the synchronizing signal.