GB621484A - Improvements in and relating to synchronising arrangements for television systems - Google Patents

Abstract

621,484. Television. FRANCE, H. DE. Feb. 12, 1942, No. 1876. Convention date, March 12, 1941. [Class 40 (iii)] In a television system in which the vision signals are amplitude-modulations of a carrier frequency, the frame synchronizing signals are transmitted by a variation of the carrier frequency and the line synchronizing signals are transmitted by amplitude-modulation of the carrier frequency, irrespective of its frequency variations. In the diagrammatic arrangement, Fig. 1, picture signals from an iconoscope Ic together with frame and line synchronizing signals from generators i, l respectively, are fed to a modulator M and a final stage E<3> of a transmitter. The frame signals i are also fed to a control device S so that during the frame signals an oscillator I generating a frequency n is connected to the transmitter arrangement E<1>, E<2>, E<3> in lieu of the oscillator I<1> generating a frequency n<1>. During the interval between the frame signals 1, Fig. 2, the valve 2 is non- conducting and the valves 3, 4 are passing current, the operation of the valve 4 preventing the valve 5 from operating so that the voltage at the point D is relatively positive and operates the valve 71 of a valve pair 6<1>, 7<1> forming the oscillator I<1> and generating a frequency n<1>. The frame synchronizing pulses 1 bias the valve 2 into operation and the valves 3, 4 are cut off. When the valve 4 becomes non-conducting, the valve 5 passes current so that the potential at the point C becomes relatively positive and effects the operation of the valve 7 of the pair 6, 7 forming the oscillator I generating the frequency n. The line-synchronizing pulses are applied to the frequencies n, n<1>. The frequencies generated by the oscillators I, I<1> are preferably amplified and multiplied at 8 so that the carrier frequencies transmitted are multiples of the frequencies n, n<1>. The carrier frequencies employed may differ by about 500,000 cycles per second. The frequencyvariation utilized for the frame synchronizing signals may be a frequency-modulation of the normal carrier.