Patent GB-1412091-A (GB)
Title: Systems for recording and reproducing colour television signals
IPC: G11B15/18
Filed: 1973-01-17
Abstract: 1412091 Colour television SONY CORP 17 Jan 1973 2437/73 Heading H4F NTSC or PAL colour television signals are recorded on a magnetic tape and subsequently reproduced so that the reproduced signals have the same field frequency (60 Hz or 50 Hz) as the original signals, but have a predetermined subcarrier frequency, irrespective of the original subcarrier frequency. To allow for the different field frequencies the magnetic heads recording the signals on the magnetic tape are rotated at different speeds for the different field frequencies of the signals which are recorded, the magnetic heads being rotated at the same speed during reproduction as they were during the respective recording. This speed change may be accomplished using a driving belt connecting respective pulleys connected to the magnetic heads and driving motor, the driving belt being movable between two positions on the pulleys, the pulleys (10, 13, Fig. 1, not shown) having different diameters at these positions. The luminance component of a signal to be recorded is frequency modulated at 22, Fig. 2, on to a carrier, and the chrominance component in frequency-converted to a frequency lower than the frequency-modulated luminance component, using a burst gate 28, two switches 29, 30 switched to positions N for recording an NTSC signal and positions P for recording a PAL signal, separate oscillators 31, 34 for producing an NTSC or PAL reference subcarrier signal in response to the separated burst signals, an oscillator 33 producing a signal at 767 kHz frequency converters 32, 27 to provide a chrominance component with a subcarrier frequency of 767 kHz. The reproduced signal is separated into its luminance and chrominance components using high-pass and low-pass filters 36 and 40, Fig. 5. The chrominance component is frequency converted at 41 to have the predetermined subcarrier frequency, which as described is the PAL subcarrier frequency, 4À43 mHz, jitter in the reproduced output being compensated for by using a phase detector 45 receiving the outputs of a burst gate 44 and a reference signal oscillator 46, to control a variable frequency oscillator 42 feeding the frequency converter 41. The resulting signal from combiner 39, Fig. 5, is, after modulation on a carrier, fed to a receiver Fig. 6, where the luminance, chrominance, and synchronizing components are separated at 58, 60, and 71 respectively. Switches 48, 49, 50 and 78 are switched to positions N when receiving an NTSC signal and positions P when receiving a PAL signal. The vertical scanning of display tube 70 is controlled by vertical oscillator 72 operating at 60 Hz for NTSC operation or by vertical oscillator 81 operating at 50 Hz for PAL operation. For PAL operation switch 78 is closed and a flip-flop 53 is controlled by the output of horizontal output circuit 76 to switch switches 51, 52 at the end of each line period, switch 78 being open for NTSC operation so that flip-flop 53 is disabled and switches 51, 52 remain in their positions shown. For NTSC operation every received line of the chrominance component is passed via switch 51 to demodulators 62, 63, the B-Y reference signal being obtained from a phase inverter 69 connected to an oscillator 68 receiving bursts from a burst gate 67 and the R-Y reference signal being obtained from a phase shifter 66 connected to an oscillator 65 receiving bursts from a burst gate 64. For PAL operations each alternate received line is passed to demodulators 62, 63 by switch 51 directly and after being delayed in one line delay line 79, the B-Y reference signal being produced from phase inverter 69 and the R-Y reference signal being produced directly by oscillator 65, of phase midway between those of the bursts fed to switch 52 directly and via phase inverter 80. In an alternative embodiment of receiver (Fig. 10, not shown), switch 51 is operated at the end of each line for both NTSC and PAL operation, a detector being included to ensure the correct phase of operation of switch 51 for PAL operation so that only those lines having the R-Y modulation axis at +90 degrees relative to the B-Y axis are passed to the demodulators, the B-Y and R-Y reference signals being derived by appropriate phase shifters connected to the output of one oscillator connected to the output of a burst gate receiving the signal from the output of switch 51. In this case the speed of the tape transport may be modified during reproduction of a recorded NTSC signal so as to provide a line period equal to that of a PAL signal and allow the use of a PAL delay line.