GB722962A - Improvements in and relating to the recording of television signals - Google Patents

Abstract

722,962. Television. BRITISH BROADCASTING CORPORATION. Sept. 11, 1953 [Oct. 23, 1952], No. 26661/62. Class 40 (3). In an arrangement for recording on intermittently moving kinematographic film pictures represented by double-interlaced television signals the signals in alternate frames are delayed by one frame period and switched, alternately and at a high rate, with signals from a, now, simultaneously occurring frame, to the control electrodes of a picture reproducing tube, the beam of which is deflected, by conventional means, to produce a non-interlaced raster having a number of lines corresponding to the number of lines in one frame and, by auxiliary means operative in the frame direction of scanning and synchronized with the signal switching, to position the beam in appropriate relative positions such that a conventional interlaced picture is reproduced, this picture then being photographed whilst the film is stationary and the film being advanced during alternate frame trace periods corresponding to the delayed frame. This arrangement allows an ordinary intermittentmotion kinematograph camera to be employed since a full frame trace period is available for the film advance. Fig. 1 shows the single embodiment and comprises a separator circuit 11 which supplies received video signals to a first switch 15 operated at frame rate and arranged to supply the video signals to a second switch 19 alternately over channels 16 and 17, the latter channel including a delay device 20 which delays the signals by one frame period. The signals of alternate frames, which now occur simultaneously at switch 19, are applied to the control electrode 23 of the picture reproducing tube 13 alternately and at a high rate (approximately 6 Mc/s.) under the control of a switching signal from a generator 24 which, synchronously with this switching supplies an auxiliary frame deflecting coil 33 with a deflecting signal having an amplitude equal to one-half the normal line pitch and a direction (i.e. " up " or " down ") which varies at the switching rate. This auxiliary deflection, which is superimposed on a normal non-interlaced raster produced by line and frame deflecting coils 31, 32 respectively, then results in the reproduction of a conventional interlaced picture which is photographed on film 28 during stationary periods thereof, the film being advanced during alternate frame trace periods corresponding to the delayed frame. To ensure that the reproduced picture has its " odd " and " even " lines correctly positioned (i.e. first line of an " odd " frame above first line of an " even " frame) the switchwave generators 18, 24 may be locked in the required phase by means of a pulse which is produced at the end of every " odd " frame. This pulse is produced by supplying pulses derived from the trailing edge of all (line and frame) synchronizing pulses and delayed by about 55Á.sec. to a "gate" circuit which is opened only during the occurrence of signal levels less than the black level. Since the delayed pulse derived from the trailing edge of the last line synchronizing pulse of each " odd " frame occurs during transmission of the first broad frame synchronizing pulse following " odd " frames (i.e. during transmission of a signal level less than the black level), the delayed pulse passed by the " gate " circuit uniquely identifies the " odd " frames. The delay device 20 may comprise: (1) an electric transmission line; (2) an acoustic transmission medium-the signals being connected into acoustic vibrations and reconverted into electric signals after traversing the required length of medium; (3) a magnetic drum or tape-the signals being reproduced with a suitable delay; (4) an electron storage surface on which the signals are recorded and subsequently scanned with the required delay to reproduce the signals, or (5) a picture reproducing device on which the signals are stored in picture form and subsequently scanned by a television camera to regenerate the signals with the required delay. By flattening the peaks of the wave supplied by generator 24 the electron beam spot may be caused to " dwell " in each " odd " and " even " line position.