Patent GB-1285475-A (GB)
Title: SIGNAL PROCESSING e.g. FOR MAGNETIC RECORDING AND REPRODUCING APPARATUS
IPC: H04N5/781
Filed: 1969-08-11
Abstract: 1285475 Television NIPPON VICTOR KK 11 Aug 1969 [14 Aug 1968] 40136/69 Heading H4F [Also in Divisions G4-G6] The invention claimed relates to video signal processing in which regular line interlace is introduced into a video signal by adjusting the phase of appropriate ones of the fields relative to the remaining fields under control of a switching signal derived from associated equalizing pulses, all the vertical synchronizing pulses being treated identically to maintain their phase relationship. A video recorder, Fig. 1, with provision for slow- and stop-motion playback comprises a magnetic disc 10 rotated by a synchronous motor 11 and two magnetic heads 14, 15 moved radially relative to the disc by stepping motors 16, 17. The disc makes one revolution for each complete field of the video signal and the system is arranged so that the first field is recorded on the outer circular top track by head 14, the second field is recorded on the outer circular bottom track by head 15 and simultaneously head 14 is stepped inwards two tracks, and the third field is recorded by head 14 while head 15 is stepped inwards two tracks. Fields are recorded alternately on the top and bottom of the disc in a similar way until the centre track is reached and recording continues by stepping the transducers alternately outward using the tracks omitted during the inward motion. When the outer track is reached the recording continues by erasing and re-recording on the inwardly-going set of tracks. The recording and playback system is shown in Fig. 3. The video signal to be recorded is applied to an F.M. modulator 24, the output of which is applied via gate 25 and amplifiers 26, 29 to the magnetic heads 14, 15. The gate is controlled by pulses from a generator 34 synchronized by external frame pulses so that alternate fields are applied to the heads 14 and 15. In the playback mode, the signals from the heads 14, 15 are applied via pre-amplifiers 37, 38 to a second gate 39 which combines them to reconstitute the signal which is applied to limiter 40 and demodulator 41. The resulting video signal is applied to a "field setting" circuit 44 which corrects the interlace during slow- and stop-motion playback. In circuit 44 the video signal is applied to F.M. modulator 46 the output of which is applied to an H/2 (half line period) delay line 47 and to a network 48 having the same frequency characteristics as the delay line, the delayed or undelayed signal is selected by a switch 49, noise is removed by a limiter 50 and the signal is applied to demodulator 51. The transducer stepping motors 16, 17 are controlled by pulse generator 34 which is provided with logic circuits arranged so that the switch 39 and motors 16, 17 operate to reproduce each field a predetermined number of times when slow motion playback is required, the number depending on the speed reduction ratio. This, however, results in consecutive fields without interlace so that further logic circuitry is provided to control switch 49 to introduce an H/2 delay when required to produce a correctly interlaced output signal. In order to prevent synchronization errors, however, the logic circuitry is arranged so that the signal is always undelayed during the vertical sync. interval. The equalizing pulses in an external reference signal are detected by a tuned circuit and utilized together with externally applied frame pulses to generate the required switching signal.