GB433295A - Improvements in or relating to television - Google Patents

Abstract

433,295. Television. RADIOAKT.- GES. D. S. LOEWE, 10, Wiesenweg, and WOLFF, H. H., 4, Heinrich Seidelstrasse, both in Steglitz, Berlin. Jan. 5, 1934, No. 389. Convention date, Jan. 6, 1933. [Classes 40 (iii) and 40 (v)] In a cathode-ray transmitter in which the speed of scanning is varied while the intensity of the ray remains constant, transmission is effected by means of frequency modulation or phase modulation in order that fading may not produce loss of synchronism. Transmitter. The light-spot formed on the screen S is projected by lens D on to the film F, and the transmitted light is focused by a condenser K on to a photocell LE, the current from which controls the valve R1 and consequently the rate at which condenser C1 is charged through the saturated rectifier Rk1 The condenser-potential controls the linescanning deflecting-plates AP1 and is also communicated via the lead M to the wireless transmitter. The end of a line is reached when the condenser C1 is fully charged, whereupon the discharge-tube Gl1 breaks down and discharges the condenser. A similar effect is produced at frame-scanning frequency by the parts R2, C2, GL2, which control the potential of the plates AP2 and are controlled through condenser C3 or through a battery by the linescanning potential. Frequency modulation and demodulation. Picture current representing the varying scanning-speed is applied to vary the inductance of an iron-cored coil in the tuning-circuit of an oscillator ; or alternatively to vary the capacity of a condenser microphone in that circuit, Figs. 2, 3, 4 (not shown). The frequencymodulated oscillations pass through band filters and amplifiers and are then radiated. At the receiver the modulated carrier is amplified, Fig. 5 (not shown), and is then applied to a set of tuned relays r, Fig. 6, each relay corresponding to a particular depth of tone in the picture and to the frequency associated therewith. The relays r may respond to high frequency or, Fig. 8 (not shown), to frequencies which have been reduced by means of a heterodyne receiver. Television receiver. The resistance of valve R8, Fig. 6, is determined by the selected relay r, and absorbs a corresponding fraction of the current passing through a saturated rectifier, Fig. 7 (not shown), similar to Rk1. and shunted upon the valve R8. The remainder of the current goes to charge a parallel condenser corresponding to C1 and so to control the linedeflection in the cathode-ray receiver. The frame-scanning deflection at the receiver is controlled by an arrangement similar to that (C3, R2, C2, Gl2, Rk2) used at the transmitter, Fig. 1. The Specification as open to inspection under Sect. 91 comprises also a method of frequency-demodulation in which a slotted disc in the cathode-ray tube is employed, Figs. 9, 9A, 9B, (Cancelled, not shown) ; and another method in which the plate circuit of a cathode-ray tube is coupled to an amplifier and cathode-ray receiver. This subject-matter does not appear in the Specification as accepted,