GB456564A - Improvements in and relating to television systems - Google Patents

Abstract

456,564. Television; valve-generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London. March 26, 1936, No. 9087. Convention date, March 26, 1935. [Classes 40 (iii) and 40 (v)] In a method of television employing interlaced scanning, in which there are generated and transmitted line synchronizing signals of substantially constant frequency and wave form and frame synchronizing signals having initial portions of substantially the same shape and which are arranged to occur in substantially the same phase with respect to the line synchronizing impulses, each frame signal has a wave form different from that of the frame signal preceding it and succeeding it and from that of the line synchronizing signals. The line and frame signals are applied to an amplifier 9 and transmitter 12 to which the picture signals from the cathode-ray tube 1 are also fed. In addition, the signals are fed to valves 34, 39 and through an oscillation generator 13 to the line scanning coil 7. The frame signals, separated by the filter 41, 42, are fed to a blocking oscillator 15, the frequency of which is slightly below that of the frame frequency. The impulses provided by the valve 16 of the oscillator 15 are fed to the grid of a valve 27 in the plate circuit of which are a condenser 23 and resistance 24 producing the saw-tooth oscillations which are passed by a valve 38 to the frame coil 6. The frame signals are also applied by means of a resistance 33 in the cathode circuit of valve 34 so that in accordance with their form they vary the plate impedance of the valve 27 and thus change the level to which the condenser 23 discharges and the form of the saw-tooth oscillation, as indicated in Fig. 9, to produce interlaced scanning for successive pictures. In a modification, Fig. 7 (not shown), the valve corresponding to valve 27, Fig. 1, is connected to two blocking oscillators, of different frequencies. Alternate frame impulses only are fed to the oscillator of lower frequency so that the condenser in the output circuit of the valve is discharged to different levels. The blocking oscillators may be of the type described in Specification 402,629 and the synchronizing signals may be produced as described in Specification 407,409. Specification 448,065 also is referred to.