GB463967A - Improvements in or relating to television transmitters - Google Patents

Abstract

463,967. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 8, 1935, No. 27805. Convention date, Oct. 26, 1934. [Classes 40 (iii) and 40 (v)] The picture received from an 'iconoscope' transmitter is found to possess an uneven shading such as shown in Figs. 6, 7. The cause is not stated, but where the picture is shaded as in Fig. 6, the picture signals taken off from the resistance 41, Fig. 1, at the transmitter correspond to the train of Fig. 8. According to the invention, correcting signals are added to the train of Fig. 8 to produce the train of Fig. 12 and render the picture evenly shaded. The correcting signals comprise (1) a saw-tooth oscillation, Fig. 9, at the line frequency which adds to the train of Fig. 8, to produce the train of Fig. 10 ; (2) a saw-tooth oscillation, Fig. 11, at the frame frequency which adds to the train of Fig. 10 to produce the train of Fig. 12 ; and (3) harmonics of the line and frame frequencies. Where the view 14, Fig. 1, is illuminated by light from a source 16 energized by alternating current, a "hum" component is added to the transmitted signals. This is compensated by adding sinusoidal oscillations at line and frame frequencies. Preferably, the frame frequency is the same as the alternating current frequency so that the " hum component produces stationary shadings on the received picture. At the transmitter, synchronizing impulses are generated at 29 and applied to saw-tooth oscillation generators 35, 39 to energize the scanning coils and plates 19, 21. Line frequency saw-tooth oscillations are taken from 39 over a lead 61 and applied to one of two bus-bars 75, 77 over (1) a circuit 65, 67, 69, 71 ; (2) a circuit 89 ... 107 producing the second harmonic ; and (3) a circuit 111 ... 131 producing a line frequency sinusoidal oscillation. Similarly saw-tooth oscillations from the frame generator 35 are applied to one of the bus-bars 75, 77 over a circuit 137 ... 145. Frame frequency sinusoidal oscillations are taken from the mains and applied over (1) circuit 151 ... 165 to one of the bus-bars ; and (2) over a circuit 179 ... 203 to produce the second harmonic of the frame frequency oscillation. A double-diodetriode valve 181 in this last circuit has its output tuned by the circuit 199, 197 to produce a strong second harmonic. The bus-bars 75, 77 are respectively connected to the inputs of valves 79, 81, Fig. 2, of the amplifier 57, Fig. 1, so that the phase of the output of the amplifier 57 depends upon the choice of busbar. The output is added to the picture signals before they enter the amplifier 45, Fig. 1. The corrected signal is amplified by valves 261, 263, Fig. 3, and then has added to it " blanking " impulses, Fig. 13, so as to produce the train of Fig. 14, in which the spurious signals y, Fig. 8, produced during fly-back are lifted above the level of the picture signals. This train is then subjected to limiting by a valve 267, Fig. 3, to produce the train of Fig. 15 to which synchronizing impulses Fig. 16, are added to produce the final signal of Fig. 17, which is modulated on to the carrier. This final signal is also applied to a monitor receiver 258 at the transmitter to enable an operator to adjust the phase and magnitude of the correcting signals to produce an evenly shaded picture. A suitable generator 35, Fig. 1 of frame sawtooth oscillations is shown in Fig. 4. The condenser 215 is charged from a source + B, -B, and is discharged by a valve 209 rendered conducting by synchronizing impulses applied to its grid. The pure saw-tooth oscillation is taken off over condenser 217, amplified at 219 and led off to the circuit 137 ... 145 of Fig. 1. The deflecting coil is however fed with the oscillation taken off over condenser 221 and amplified at 225. This oscillation comprises the pure saw-tooth oscillation generated across condenser 215 together with a peak oscillation developed across the resistance 213 and produces a pure saw-tooth current in the deflecting coil.