Patent GB-1490106-A (GB)
Title: Video magnetic tape recording and reproducing apparatus
IPC: H04N9/70
Filed: 1974-10-14
Abstract: 1490106 Colour television MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 14 Oct 1974 44469/74 Heading H4F A video signal recording and reproducing system includes a single colour killer detector circuit constituted by a 90 degree phase shifter 32 and a synchronous detector 33 which controls colour killer circuits 11 and 28 in the recording and reproducing sides respectively. An NTSC signal to be recorded is separated into luminance and chrominance components by low-pass filter 2 and band-pass filter 6, the luminance component being supplied via a frequency modulator 3 and a high-pass filter 4 to an adder 12: when recording a monochrome signal, as indicated by the colour killer signal from synchronous detector 33, a switch 5 supplies the output of modulator 3 directly to adder 12. The chrominance component is converted into a lower frequency band by a heterodyne circuit 8, the output of which is supplied via colour killer circuit 11 to adder 12. During recording the output of adder 12 is supplied via a selection switch 14 to a magnetic recording head 15 and the output of heterodyne circuit 8 is supplied via a switch 31 to a low-pass filter 20. During playback low-pass filter 20 receives the playedback signal from magnetic recording head 15 and separates the chrominance component therefrom. The output of low-pass filter 20 is supplied to heterodyne circuits 21, 26. The output of heterodyne circuit 21, at the sum frequency of the output of low-pass filter 20 and the output of a reference oscillator 22, is supplied to a burst gate circuit 23 which supplies separated bursts to 90 degrees phase shifter 32 and a phase comparator 24. The phase comparator 24 receives its other input from a voltage controlled oscillator 25 which it controls. The output of voltage controlled oscillator 25 is supplied to heterodyne circuit 26 to derive a filter-free chrominance component of NTSC subcarrier frequency which is supplied via colour killer circuit 28 to an adder 29. Synchronous detector 33 receives inputs from phase shifter 32 and oscillator 25; phase shifter 32 may alternatively be connected between oscillator 25 and synchronous detector 33. The luminance component of the playedback signal is separated by a high-pass filter 17, demodulated at 19 and supplied to adder 29; on play-back of a monochrome signal, as indicated by the colour killer signal from synchronous detector 33, switch 18 connects the output of play-back amplifier 16 directly to demodulator 19. In alternative embodiments switch 31 is omitted, the output of heterodyne circuit 8 being connected to the input of low-pass filter 20, a unidirectional transmission circuit (37,  Figs. 6a, 7, not shown) being included between playback amplifier 16 and low-pass filter 20 or between playback amplifier 16 and the inputs of high-pass filter 17 and switch 18. In a further embodiment (Fig. 8, not shown) the output of heterodyne circuit 8 is connected to the input of low-pass filter 20, a unidirectional transmission circuit (37) being connected between playback amplifier 16 and low-pass filter 20. Heterodyne circuit 21 is omitted and the output of low-pass filter 20 is supplied to heterodyne circuit 26 via an automatic chrominance level control circuit (38) which is bypassed by a switch (SW5) during recording. The burst gate circuit 23 receives its input from the output of heterodyne circuit 26, and phase comparator 24 and synchronous detector 33 receive inputs from reference oscillator 22 rather than voltage controlled oscillator 25.