Patent GB-709349-A (GB)
Title: Improvements in colour television systems
IPC: H04N9/44
Filed: 1951-09-28
Abstract: 709,349. Television. RADIO CORPORATION OF AMERICA. Sept. 28, 1951 [Oct. 2, 1950], No. 22702/51. Class 40 (3) In a line or field sequential colour television system, selected line sync. pulses, e.g. 26, Fig. 1, are "notched" to identify the colour of the signal transmitted during the succeeding line period. In the first embodiment, Figs. 1 . . . 4, in which any line colour sequence may be employed, the spacing of the notches from the leading edges of the red, blue and green sync. pulses 26, 28 and 30, Fig. 1, are different and at the receiver, Fig. 2, the video signal is applied in parallel from amplifier 42 through gates 44, 46 and 48 to red, blue and green colour reproducers, the gates being controlled by outputs from a decoder 52 fed with notched sync. pulses from the sync. separator 50. If all the lines in one field represent the same colour, the system is field sequential. Alternatively one colour may be identified by an un-notched sync. pulse. In the second embodiment, Figs. 5 ... 9, employing conventional odd line interlace alternate fields are comprised entirely of green lines and the interlace fields comprise alternate red and blue lines, the red lines being identified by a notched line sync. pulse and the green fields being the ones in which the leading edges of the line and field sync. pulses do not coincide. First embodiment.-As shown in Fig. 1 the outputs from the red, blue and green cameras 2, 6 and 10 are applied to an adder 34 via gates 4, 8 and 12 which are opened sequentially by gating pulses from a sequence selector 16 coupled to the sync. generator 14 the gating pulses and sync. pulses being also applied to a " notching " device 24 to produce corresponding notched sync. pulses 26, 28 and 30. A notched sync. pulse is produced, Fig. 3 (not shown), by applying a positive gating pulse to trigger a transitron square wave generator whose negative anode output is differentiated and applied to trigger a second transitron giving a narrow negative delayed notch pulse which is combined with a positive sync. pulse, the red, blue and green gating pulses being applied to separate first transitrons producing output pulses of different duration and the second transitron being common to the three stages. In the receive decoder, Fig. 4 (not shown), positive sync. pulses are applied in parallel to trigger three transitrons producing negative square waves with durations equal to the red, blue and green delays respectively which are differentiated and applied together with negative sync. pulses to corresponding coincidence pentodes coupled to flip-flops producing positive gating pulses of line period duration which are applied to gates 44, 46 and 48, Fig. 2. Second embodiment.-As shown in Fig. 5, the outputs from the red, blue and green cameras, 200, 204 and 208 are applied through gates 202, 206 and 210 to an adder 242. Negative horizontal and vertical sync. pulses from generator 212 are applied repectively to opposite ends of serially connected resistors 222, 224 and horizontal sync. pulses from the upper end of resistor 222 are applied to two inputs of a counter 214 comprising two interconnected trigger pairs, Fig. 7 (not shown), producing push-pull square wave outputs of half the line frequency which are applied through amplifiers 230, 232 and inverters 234, 236 to gates 202, 206 respectively so that the gates are alternately opened for a line period. Vertical sync. pulses are applied from the lower end of resistor 224 to a first input of a similar counter 218 and horizontal and vertical sync. pulses of half amplitude are applied from the junction of resistors 222, 224 to the second input of the counter which responds only to coincident half amplitude horizontal and vertical sync. pulses occurring every alternate field so that counter 218 produces a square wave of half the field frequency which is applied through amplifier 240 and inverter 238 to gate 210 which is thus opened during alternate fields, i.e. the green fields. Amplifiers 230, 232 and 240 have a common cathode bias impedance, Fig. 7 (not shown), so that, when amplifier 240 is conductive (i.e. gate 210 open), amplifiers 230 and 232 are blocked and gates 202 and 206 are shut. The negative red gating pulses from amplifier 230 are applied through inverter 247 to the notching device 244, Fig, 8 (not shown), together with negative horizontal sync. pulses so that only the red sync. pulses are notched. At the receiver, Fig. 6, the video output from detector 246 is applied in parallel through gates 248, 250 and 252 to the red, blue and green colour reproducers and local horizontal and vertical sync. pulses derived from the horizontal and vertical timebase generators 251, 253 coupled to sync. separator 249 are applied to counters 214', 218' which together with their associated amplifiers 230<SP>1</SP>, 232<SP>1</SP>, 240<SP>1</SP> and inverters 234', 236', 238' and similar to the corresponding components at the transmitter except that a trigger pulse derived from the red notched sync. pulse in decoder 254, Fig. 9 (not shown), is applied to the second input of counter 214<SP>1</SP> so that the receiver gates 248, 250 and 252 are opened synchronously with the transmitter gates 202, 206 and 210.