GB514650A - Improvements in or relating to television or like systems - Google Patents

Abstract

514,650. Television; valve amplifying cir- 'cuits. FERNSEH AKT.-GES. May 12, 1938, No. 14184. Convention date, May 12, 1937. [Classes 40 (iii) and 40 (v)] In order to obtain a positive reproduction after transmission from a negative film or vice versa, whilst retaining the original gradation of light and shade, television or like signals are reversed by passage through a device which transforms signals having increasing voltage stages, the differences of which increase (or decrease) logarithmically into signals having increasing voltage stages, the differences of which decrease (or increase) logarithmically, i.e., the reversal stage has a double logarithmic characteristic. This may be achieved by an amplifier or attenuator with a characteristic as shown in Fig. 4 and such an amplifier can be designed by connecting in parallel three valves or sets of valves having respectively small amplification, large amplification, and medium amplification, their characteristics being represented by the curves a, b, c, Fig. 5, of which c is preferably curved. Fig. 6 shows such a combination of three valves 1, 2, 3 having variable anode impedances 4 .. 6 and variable grid-bias resistances 7..9 by which the individual characteristics may be varied to obtain the desired overall characteristic. Alternatively, the screen-grid voltages may be variable. The characteristic may also be adjusted to compensate for the gradation curve of the film emulsion and for non-linearity of characteristic of the cathode-ray tube. The invention is applicable to the reversal of an image of a sound track and to picture telegraphy and the transmission of photographs.