Patent GB-685496-A (GB)
Title: Colour television system
IPC: H04N11/12
Filed: 1950-11-24
Abstract: 685,496. Multiplex pulse signalling. RADIO CORPORATION OF AMERICA. Nov. 24, 1950 [Dec. 1, 1949], No. 28790/50. Class 40 (v) [Also in Group XL (b)] In a pulse multiplex communication system, the signal from at least one source is diluted by energy obtained from at least another source, so that the amplitudes of the sampled pulses tend to become uniform, the dilution being removed at the receiver. The invention is described as applied to a dot interlace colour television system to reduce dot structure in the received picture and to produce signals which are particularly adapted for black-and-white receivers. At the transmitter, the green, red and blue cameras, 18, 20, 22, Fig. 1, respectively feed signals to the sampling commutator 10, the output of which, consisting of interlaced amplitude-modulated green, red and blue signal pulse trains, is passed through the adder 60 to the radio transmitter 54. Low-pass filters 2, 4, 6 are interposed in the channel paths. In addition, the green, red and blue signals are added in circuit 56 passed through the high-pass filter 58 and fed direct to the adder 60 to provide the picture detail. The sync. signal generator 36 controls the cameras and the commutator drive 32 through the interlace oscillator 34. The " diluter " 23 for mixing the channel signals is described later. At the receiver, the video pulses from the radio receiver 60, Fig. 2, are distributed by commutator 72 to the channel low-pass filters 78, 79, 80, adders 94, 95, 96 and reproducers 88, 90, 92, respectively. The total video receiver output is also fed to the high-pass filter 93, commutation frequency rejector 140 and adders 94, 95, 96 to provide the picture detail. The sync. separator 64 controls the sweep signal generator 66, interlace oscillator 68 and commutator drive 70. The intensifier circuit 81 corresponds to the " diluter " at the transmitter and restores the channel signals to their original form. The circuit of the diluter 23 in one form produces signals according to the following equations. G Ld =G L ; R Ld =K 1 (R L + G L ) and B Ld =K 2 (BL+R L +G L ), where G Ld , R Ld  and B Ld  are the diluted channel outputs, G L , R L  and B L  are the channel inputs and K 1  and K 2  are constants. The three inputs are applied to valves 168, 172, 178, Fig. 6, respectively, from the anodes of which are taken the diluted outputs. A variable portion of input G L , determined by the setting of potentiometer 180 is fed to valve 170, the valves 170, 172 having a common output load resistance. The input of valve 178 is supplied with a proportion of the combined G L  and R L  channel signals through valve 174, in addition to the B L  channel signals. At the receiver, the restoring circuit 81, comprises valves 190, 192, 196, Fig. 7, to which the diluted channel inputs G Ld , R Ld  and B Ld , respectively, are applied, and from which the " intensified " channel outputs G Li , R Li  and B Li  are taken. Part of the output of valve 190 is fed through resistance 198 to the input of valve 192 to remove the green component present in input K Ld . The output B Li  is obtained by subtracting from input B Ld  a portion of the input signal R Ld  derived from potentiometer 202, valve 194 and resistance 204. Diluters and intensifiers following other laws are discussed and examples described, Figs. 10, 11 (not shown).