GB758085A - Improvements in or relating to television and telecinematograph systems - Google Patents

Abstract

758,085. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Feb. 24, 1954 [March 12, 1953], No. 6895/53. Class 40 (3). A system for photographically recording pictures for subsequent projection or for simultaneous or subsequent television transmission with interlaced scanning comprises: a pick-up tube arranged to scan the picture with a spot subject to field, line and wobble deflections, the field and line deflections being such as to produce interlaced scanning and the wobble deflection being transverse to the line deflection and of such amplitude that the whole picture area is explored in each field, a picture reproducer tube fed with signals from the pickup tube and subject to deflections similar to those of the pick-up tube, and means for photographing the reproducer tube. Since the the whole of the picture information is derived and reproduced in each field, the recording may be effected by a standard intermittentmotion camera photographing only one field per picture. Adequate time is made available therefore for the film pull-down operation. In the case of a system operating with British standards to record or film at 25 frames per second, the camera merely records alternate fields. In the case of a system operating with United States standards, the camera records two out of every five fields. Either a mechanical shutter or electronic blanking is employed to occult the unwanted fields. Where transmission is effected simultaneously with the recording by conventional standards (i.e. without wobbling), a gating stage is employed to pass signals to the transmitter at the instants when the pick-up tube scanning spot is traversing the picture areas corresponding to the lines of the conventional scan. The signal derived and employed for recording may be of considerably higher quality and resolution than that provided by sampling for simultaneous transmission. Fig. 5 shows an arrangement in which the wobbling deflections at the pick-up and reproducer tubes are effected independently without synchronism. The picture is analysed by pick-up tube PU and the signals passed to a wide-band amplifier WBA. The pick-up tube wobbling action is controlled by an oscillator WO which also synchronizes the action of a gating unit SGU<SP>1</SP>. The gating action takes place at three times the wobble frequency and is effective to cause pulses to be derived at the instants X, Y and Z, as shown in Fig. 6. In Fig. 6, the solid curves indicates the wobble deflection effected in one field and the dotted curve the deflection effected in the interlaced field. The pulses X, Y and Z are passed respectively into separate narrow-band channels XC, YC and ZC. The channels feed into a unit RSA at the recording equipment where the received signal trains are re-sampled under the control of pulses from a local oscillator RWO operating independently of oscillator WO. The re-sampled signals are combined and pass through a wide-band amplifier WBA<SP>1</SP> to a reproducing tube in unit RU the wobble deflection of which is controlled by oscillator RWO. Reproducing unit RU incorporates the recording camera. Separate control of the gains of channels XC, YC and ZC may be provided to equalize the brightness of the reproduced X, Y and Z signals. Alternatively equalization may be effected by control of the widths of the sampling pulses. Signals for simultaneous transmission by transmitter T are taken from the output of channel XC and, as may be seen from Fig. 6, correspond to those which would be derived by a conventional interlaced scan. Fig. 4 (not shown), illustrates a further arrangement in which the output from the pick-up tube is passed through a wide-band amplifier directly to the recording unit and the wobbling deflection of both the pick-up and reproducing tube is controlled by a common oscillator. The output of the amplifier also feeds a gate stage which passes signals to a transmitter at the instants corresponding to a conventional interlaced scan. As an alternative to using a sinusoidal wobble deflecting wave as shown in Fig. 6, a three-stop wave may be employed, Figs. 2a and 2b (not shown), illustrating two examples. The amplitude of wave is preferably varied in proportion to the rate of change the field deflecting wave as described in Specification 736,536 to allow for unavoidable non- linearities in the field deflection. Reference is also made to the use of dot immobilization.