Patent GB-1493876-A (GB)
Title: Recording and/or reproducing system
IPC: G11B20/02
Filed: 1975-02-17
Abstract: 1493876 Colour television recording SONY CORP 17 Feb 1975 [18 Feb 1974] 6621/75 Heading H4F The invention is concerned with the magnetic recording and play-back of colour television signals employing apparatus of the type disclosed in Specification 1,477,466 and is particularly directed to the provision of means for controlling the switching circuits that periodically reverse the phase of the chrominance sub-carrier during certain line scan periods. The invention is applicable to the recording and play-back of colour television signals of the NTSC or of the PAL system. Referring to Fig. 10, which shows a recording section and a play-back section each including a reversing switch 33, the sections being selected by positioning switches linked 91, 92 and 93 in the R (recording) or P (play-back) positions respectively, each switch 33 is required to be operated, in the case of NTSC signals, as shown by waveform Sc (Fig. 11F). This waveform, which is derived from the Q output of a J-K flip-flop 104 causes the switch arm of switches 33 to remain in one position for the whole of alternate vertical (field) periods of the television signal (to be recorded on or derived from the magnetic tape 11) whilst during the intervening field periods it is switched between the two positions alternately at the horizontal (line) period. The output of the switches 33 then consists of one phase of the chrominance sub-carrier during alternate field periods and the one phase and the opposite phase of the sub-carrier during alternate line periods respectively of the intervening field periods. In the generation of the waveform Sc a pulse generator 101 responsive to the passage of the recording heads 19, 21, generates pulses Sp (Fig. 11A) which trigger a monostable multivibrator 102 to produce a signal SM (Fig. 11 B) which has a level "0" during recording by head 19 and a level "1" during recording by head 21. The signal SM is supplied to the D-terminal of a D-type flip-flop 103 the timing terminal T of which receives vertical synchronizing signals Vs (Fig. 11c) from the vertical synchronizing separator 37 and the output of flip-flop 103, consisting of the signal SD (Fig. 11E), is supplied to the J-input of a J-K flip-flop 104. The timing terminal T of the latter is supplied with the horizontal rate synchronizing signal PH (Fig. 11D) derived from a monostable multivibrator 105 supplied from the horizontal synchronizing separator 36 and the Q output then provides the signal (waveform) Sc. Fig. 12 shows a second embodiment in which the J-K flip-flop 104 of Fig. 10 is replaced by a T-type flip-flop 106 the timing input T of which is supplied with the composite synchronizing signal QS (Fig. 13C). In this embodiment the timing input T ofthe D-type flip-flop 103 is supplied with the vertical synchronizing signal VSD (Fig. 13D) and the output SDD (Fig. 13E) is supplied to the RD input of flip-flop 106 which produces the required output Sc (Fig. 13F). When PAL signals are involved the switching waveform should reverse during alternate pairs of line intervals and to produce such a waveform the circuit of Fig. 10 is modified, as shown in Fig. 15, by the addition of a second J-K type flip-flop 107 the J input of which receives the SD output of flip-flop 103 and the timing input T of which receives the Sc (Fig. 17A) output of the first J-K flip-flop 104. The Q output of the second J-K flip-flop 107 then consists of the required switching waveform Scp (Fig. 17B). A modification of Fig. 15 (analogous to the modification provided by Fig. 12 in the case of the NTSC signal) is shown in Fig. 16. As an alternative to including reversing switch 33 in the path of the chrominance sub-carrier, it may be included between the oscillator and balanced modulator 31 so as to reverse the phase of the carrier signal from the oscillator.