| 摘要 |
1516734 Colour television RCA CORPORATION 15 Sept 1975 [28 April 1975] 37850/75 Heading H4F A record-reproducer system for playback of a record medium 11 of successive images is provided with apparatus for providing compensation for signal drop-out. The said system includes a pickup head 13 for recovering from said medium an FM signal having an instantaneous frequency representative of a composite video signal, FM detecting means 17 coupled to head 13 for deriving, from said FM signal, said composite signal having a luminance signal component, and means 100 for maintaining synchronization between said pick-up head and said record medium. In the absence of signal drop-out, detected by drop-out detector 19, the video signal is applied by a switch 21 to a video output 25 and to the input of a delay network 101. When a dropout is detected, switch 21 is moved to cut off the video signal from output 25 and network 101. At the same time, a switch 23 is moved to connect the delayed signal to output 25 and to the delay network input. On sensing of the drop-out, a one-shot multivibrator 37 is triggered. Multivibrator 37 and detector 19 are coupled to the inputs of an AND gate 55. If the drop-out lasts for longer than a predetermined number of line periods, multivibrator 37 causes switch 23 to move so that the output of network 101 is no longer applied to output 25 and the network input. At the same time gate 55 is activated to couple a grey reference signal generator 57 to output 25 by means of gate 59. This grey signal is coupled to output 25 until the end of the drop-out. The video signals may include a chrominance component and be of the NTSC type. The network 101 contains a low-pass filter 29 for the luminance component and a band-pass filter 31 for the chrominance component, the phase of the latter component being altered by 180‹ in an inverter 33. The delay signal components are added in a summing unit 35 to produce a substitute signal. The demodulated video output signal is also coupled to the means 100 for maintaining synchronization between the pickup head and the record medium, which comprises a magnetic tape. Instead of a grey reference level, a zero signal level may be used. |
