Patent GB-1407238-A (GB)
Title: Magnetic recording and or reproducing system
IPC: H04N9/86
Filed: 1972-11-13
Abstract: 1407238 Recording television signals SONY CORP 13 Nov 1972 [19 Nov 1971 22 Nov 1971] 52244/72 Heading H4F In the recording of a standard colour television signal comprising a luminance signal in a low frequency range, a chrominance signal in a higher frequency range centred about a high carrier frequency and a burst signal at said high carrier frequency, the chrominance and burst signals are frequency shifted to a lower range and the shifted burst, in combination with the luminance signal is modulated on to a second high carrier frequency to give a compound modulated signal in a frequency range higher than the lowered range of the chrominance signal and burst. Such readjustment of the burst frequency makes it less subject to interference. The luminance signal is separated out from the whole signal at 1, Fig. 1, by a low pass filter 2. The chrominance and burst signals are separated out by a band pass filter 4 and passed, via a grain controlled amplifier 5 to a mixing stage 6 where, by mixing with the output of oscillator 7, the signals are lowered in frequency such that the carrier and burst frequency become 560 kHz. The frequency lowered signals are selected by low pass filter 8 and the chrominance signal and burst fed to mixer 14. The burst signals at 560 kHz are passed via gate 9 enabled by a burst gate generator 11 operated by line sync pulses from separator 10. The gated burst signals are detected in amplitude at 16 to give an a.g.c. signal for amplifier 5, and are also mixed with the luminance signal in mixer 3. The output of mixer 3 is frequency modulated at 12 on to a high frequency carrier and the resultant signal mixed with the chrominance signal and burst at mixer 14. The burst signals may be partly extracted from the chrominance frequency range before the frequency shift Fig. 2 (not shown). To replay the recorded signals, the composite, signal, from replay head 20, Fig. 3, is separated out into the frequency modulated component and the frequency shifted chrominance/burst component by high pass and low pass filters 22 and 28 respectively. The frequency modulated signal is demodulated at 23 and the burst signal and luminance signal directed along respective paths 31 and 25. After undergoing a system compensating delay at 26 the luminance signal is fed to one input of mixer 27. Path 31 comprises a burst gate enabled by the line sync pulses produced by sync separator 32. The frequency shifted chrominance and burst signals, after gain controlled amplifier 29, are frequency shifted at 30 up to their normal values for addition to the luminance signal at the mixer 27. The signal at 4À14 mHz for the upwards frequency shift is supplied by a frequency converter 36 by the addition of a 3À58 mHz output from oscillator 35 and a controlled 560 kHz signal from controlled oscillator 37. The burst signal from gate 31 is converted up at 34 to a nominal 3À58 mHz by the output of converter 36 and is then used in a phase controlled loop comprising phase detector 39, controlled oscillator 37, converter 36, oscillator 35, to ensure that the burst from converter 30 is exactly at 3À58 mHz. To save space on the recording tape only every other line of chrominance signal may be recorded, Fig. 4 (not shown), with a one line delay circuit in the replaying circuit reconstituting the missing lines, Fig. 5 (not shown).