Patent GB-1265200-A (GB)
IPC: H04N9/83
Filed: 1969-10-07
Abstract: 1,265,200. Colour video signal recording and reproduction. SONY CORP. 7 Oct., 1969 [7 Oct., 1968], No. 49175/69. Heading H4F. In a video magnetic recording and reproducing system of the kind described in Specification 1,254,564 in which the recorded signal is in the form of a frequency modulated luminance signal, a chrominance signal frequency-corrected to a position below the F.M. luminance signal, and a pilot signal, means are provided for disabling the pilot signal generator and the chrominance frequency converter during recording in the absence of the burst signal and for disabling the chrominance frequency converter during replay in the absence of the recorded pilot signal. As shown, Fig. 4, in the recording mode an NTSC composite video signal is applied to input terminal 1, and the luminance component is applied via amplifier 2a and delay element 3 to a frequency modulator 4, the resulting signal being applied via a high-pass filter 5 and an amplifier 6 to a combining unit 15. The chrominance signal is removed by means of a trap T connected to the transmission line between amplifier 2a and delay element 3 by means of a switch St. The chrominance component of the composite video signal is selected by a bandpass filter 7 and applied to a frequency converter 8 and to a burst pick-up circuit 9 which feeds a detector D the output of which is applied to a gain control circuit 38 which controls the amplitude of the chrominance signal passing through filter 7. The output of detector D is also applied to a D.C. amplifier 37 which controls the operation of switches St, Sc1 and Sc2. A freerunning oscillator 10 at the chrominance subcarrier frequency (3À58 MHz) is mixed with a signal Fc (1À06 MHz) and the resulting sum applied to frequency converter 8 to shift the carrier frequency of the chrominance signal to 1À06 MHz. This signal is combined with a pilot signal generated by oscillator 14a, having a frequency of one-third that of signal Fc, and applied to the combining circuit 15 and thence to the recording head 16. The signal is also applied over switch S1 to replay amplifier 22 and the pilot signal is selected by bandpass filter 28 and applied to a frequency multiplier 31 the output of which provides the 1À06 MHz signal Fc. When a monochrome signal is applied to terminal 1 no colour burst signal is applied to detector D and switch St disconnects the chrominance signal trap T from the luminance channel, and switches Sc1 and Sc2 disconnect the outputs of the oscillators 10 and 14a from the chrominance circuit. When the switches S1, S2, S3 and S4 are moved to the replay position the reproduced signal is applied to amplifier 22, the frequency modulated luminance signal is selected by high-pass filter 23 and applied to limiter 24 and demodulator 25, the output of which is connected to combining circuit 35. The pilot signal is selected by bandpass filter 28, the output of which is detected and applied to a D.C. amplifier 38 which energizes a relay RL which connects a power supply E to the chrominance channel 26, 27, 30. The chrominance signal is selected by a bandpass filter 26 and applied to a variable-gain amplifier 27, controlled by the rectified pilot signal, to a frequency converter 30. The pilot signal is also applied to frequency multiplier 31 to produce a 1À06 MHz signal Fc which is mixed with the output of oscillator 10 in mixer 11 the output of which is applied to frequency converter 30 via filter 36. The chrominance signal is thus converted back to its normal frequency (3.58 MHz) and combined with the demodulated luminance signal to produce a reconstituted composite video signal at terminal 34. If a monochrome signal is being reproduced the pilot signal is absent and consequently relay RL is unenergized and the power supply is removed from the chrominance channel 26, 27, 30.