GB1488407A - Method for reversal of the direction of tape movement in a tape recorder during playback - Google Patents

Abstract

1488407 Reversing tape transports BASF AG 18 Feb 1975 [19 Feb 1974] 6768/75 Heading G5R In a method of reversing the direction of movement of a magnetic tape in a longitudinal track video tape recorder (VTR) during playback operation, a high frequency signal of a specific duration is recorded on the tape, during recording operation of the VTR in which the video signal is recorded as a carrier frequency modulated by the video signal, the recording of such high frequency signal commencing at the moment when a reversal of direction of the tape is initiated by the tape transport of the VTR and the frequency of such high frequency signal being above the highest frequency of the recorded carrier frequency modulated by the video signal, and a control signal for initiating tape drive reversal during playback is derived whenever a signal of frequency above the highest frequency of the recorded carrier frequency modulated by the video signal and of duration greater than a predetermined time period, which is shorter than said specific duration, is detected on the tape during playback. The tape transport has a capstan 6 drivingly engaging the peripheries of tape packs 8, 9 rotatable on carriages 14, 15 movable along a line through the axis of capstan 6 with pack 9 being in a cassette 10, and a magnetic head 12 transducing tape 13 at an air-bearing tape guide 11. During recording of video and audio signals on longitudinal tracks on tape 13, initiation of tape transport reversal is effected when carriage 14 or 15 operates microswitch 17 or 18 respectively, such operation triggering a delay circuit (2), Figs. 2, 4 (not shown), giving a delay of about 1À5 sees., the actual reversal operation commencing at the next vertical sync. pulse (in the video signal being recorded) after the end of said delay and taking slightly under 80 msec. for PAL systems (83-35 msec. for NTSC). The local oscillator of a frequency modulator (21), Fig. 4, normally giving a carrier signal frequency modulated by the video signals with 2-4 MHz deviation, is controlled by a coincidence circuit (24), with inputs from delay (2) and vertical sync. detector (23) to give an output signal to the record head with a frequency in the range 5 to 5À5 MHz and starting at the initiation of the actual reversal and lasting for a preset period of at least 200 Ásec. and not greater than about 80 msec. This signal is outside the response range of current playback heads with about 0À4 micron gap and 120 i.p.s. tape speed. During playback, the video head 25, Fig. 5, output is passed via a filter 26, passing the 2-4 MHz signals, to a known form of dropout detector 27 giving a grey colour video signal output whenever a dropout is sensed. The 5 to 5À5 MHz reversal initiating signal on the tape is also sensed as a dropout and is distinguished from ordinary dropouts by a timing circuit 28 which, whenever a dropout lasts for more than a predetermined period, e.g. 200 Ásec., operates a switch 29 to enable tape drive reversal means 30.