GB1208704A - Improvements in or relating to colour television transmitters - Google Patents

Abstract

1,208,704. Colour television. MARCONI CO. Ltd. 18 June, 1969 [28 June, 1968], No. 30967/69. Heading H4F. In a colour television transmitter the video signals to be transmitted are distorted, in order to compensate for distortions which will later be introduced by the transmitter chain, by an arrangement including three non-linear video paths. The video signals are fed via an input amplifier 1 with associated D.C. restorer 2 to a frequency power distributer 3 which provides at U 1 and U 2 two phase opposed outputs. These outputs are fed as shown to the non-linear video paths 4, 5 and 6. In path 4 the signal is pre-distorted independently of its frequency to obtain correction of differential gain in non- linear distorting circuit RD4 which comprises a plurality of parallel circuits each including a distorting passive element, e.g. a diode, and an additional parallel circuit of adjustable attenuation (Fig. 2, not shown). In path 5 the signal is distorted by a non-linear distorting arrangement RD5 (similar to RD4) which is followed by distorting means QL having a linear phase characetristic providing compensation for differential phase correction. Circuit QL comprises an inductance, a capacitor and a resistance in parallel (Fig. 3, not shown) and provides a signal vector which is 90 degrees out of phase. In path 6 the signal is distorted by a non-linear arrangement RD6 (similar to RD4 and RD5) and is then subjected to linearity correction by means of a band clipping circuit QF comprising two band-rejector circuits (Fig. 4, not shown) which have a linear phase characteristic over the whole signal band. To decouple the three paths, low input impedance amplifiers 40, 50 and 60 are connected as shown. Delay lines T 1 and T 2 compensate for the time delays introduced by circuits QL and QF. The output from T 1 is in phase quadrature to the output from 50 and thus network 7 combines the two distorted signals without any effect on the amplitude of the signal. Combiner 8 is designed to provide an impedance match with coaxial line 9 leading to the transmitter chain.