Patent GB-1064049-A (GB)
Title: Colour television system with sequential chrominance dot signal
Inventor: PTACEK MILAN
IPC: H04N11/12
Filed: 1964-08-10
Abstract: 1,064,049. Colour television. VYZKUMNY USTAV ROZHLASU A TELEVIZE PRAHA. Aug. 10, 1964, No. 32467/64. Heading H4F. The invention relates to a colour television system in which the colour information carrying signals are transformed into a signal which is amplitude modulated in such a manner that the upper modulation envelope carries one colour carrying signal, and the lower modulation carries the other colour carrying signal, the signal being frequency modulated on to the usual subcarrier of frequency 4À43 Mc/s. and added to the luminance signal before transmission. In the transmitter, Fig. 4, the fundamental colour signals are directly used as the colour information carrying signals, although other signals may be used, e.g. colour difference signals. In matrix unit 1 the luminance signal E<SP>1</SP>y is formed and the signals E<SP>1</SP>R and E<SP>1</SP>B are passed through lowpass filters 2 and 3. In auxiliary modulator 5 ignals E<SP>1</SP>R and E<SP>1</SP>B modulate an auxiliary arrier of frequency approximately 1À4 Mc/s. so that its positive envelope is modulated with the signals E<SP>1</SP> R  and its negative envelope with signal E<SP>1</SP> B , the signals being partially mixed in device 4 in order to pre-correct " cross-talk " which would occur during demodulation in the receiver. The output signal from modulator 5 then passes through low-pass filter 6 and is frequency modulated on to the main colour sub-carrier in modulator 7, and after frequency filtration in band-pass filter 8 is added in circuit 9 to the delayed luminance signal E<SP>1</SP>y to which has been added synchronizing signals Ess, to form the complete composite colour signal E<SP>1</SP> t . The output signal from modulator 5 is shown in Fig. 1d, the signal being switched over progressively over the colour picture elements between both colour carrying signals, e.g. A 1 (t) and A 2 (t) and being of the form (A 1 - A 2 )+(A 1 +A 2 ) cos w p t where W p  is the angular frequency of the auxiliary carrier, i.e. 2#1À4 Mc/s., the upper side-band being partially limited. To obtain a compatible black and white picture the phase of the frequency modulated signal is periodically switched through 180 degrees for every line and frame. Modulator 5 comprises phase inverters, pushpull modulators, gated clamp circuits for D.C. restoration during the blanking pulses and an adding stage, Fig. 5 (not shown). In the receiver, Fig. 6, the colour sub-carrier is suppressed in the luminance channel by filter 1, the luminance signal being delayed in stage 2, and the frequency modulated colour sub-carrier is obtained by means of band-pass filter 3. After amplitude limitation in limiter 4 the subcarrier is rectified in frequency discriminator 5 to form the colour carrier signal and then demodulated in device 6, Fig. 7 (not shown), including two diodes polarized in opposition to each other and two low-pass filters. To restore the colour signals E1 R , E<SP>1</SP> G  and E<SP>1</SP> B  highfrequency components of the luminance signal E<SP>1</SP>y from band-pass filter 7 are added in a suitable ratio to components E<SP>1</SP>R and E<SP>1</SP> B  before the signals are fed to matrix circuit 8.