Patent GB-542436-A (GB)
Title: Improvements in arrangements for controlling the transfer of signals, particularly applicable to television
IPC: H04N5/265
Filed: 1940-04-25
Abstract: 542,436. Television. PHILCO RADIO & TELEVISION CORPORATION. April 25, 1940, No. 7465. Convention date, May 11, 1939. [Classes 40 (iii) and 40 (v)] In a fade-over arrangement for television and other purposes, the transfer means is controlled by a signal derived from a wave whose form is a pre-determined function of time, the duration of the control signal being determined by the intervals during which the wave exceeds a particular amplitude level. These intervals may be determined manually by varying the grid bias applied to a valve in the circuit which derives the control signals from the wave of pre-determined form. Control signals of opposite phase may be applied to transfer means in each picture channel, so that as one picture is faded in the other is faded out. In the system described in detail, the control signals are derived from a wave r, Fig. 2, of triangular form, the duration d of the control signal being determined by the interval during which the wave form exceeds a particular amplitude A. During the intervals BC, DE, and FG, the video signals in one channel s are cut out as shown in full lines; the signals in channel t being cut out during the intervals BD and EF, so that the combined signal shown at u contains part of each picture. By varying the period DE, the proportion of each picture can be determined. Fig. 4 shows the system as a whole. Picture signals from cameras I, II pass through video amplifiers and blanking-out amplifiers to the combining amplifier and modulator. Impulses 1, which may be of line or frame frequency, derived from the synchronizing &c. impulse generator S, are converted at G into a triangular wave 2, from which control impulses such as 3, 4, 5, are derived by the " microtone ' M, the duration of these impulses being determined by the setting of the fading control bias FC. The impulses are shaped at S, and impulses of opposite phase are produced at P so as to control the blanking-out amplifiers in opposite senses. By using triangular waves of different form, frequency, and phase separately or in combination various fade-over schemes can be produced, Fig. 1 (not shown). By simultaneously varying the direct-current component, additional fade-over patterns may be obtained, Fig. 12 (not shown). Producing impulses of triangular waveform. Impulses 1, Fig. 5, are converted by valves 10, 16 with resonant plate circuits into sine-wave voltages 13, which are converted by limiting valves 17, 20 into substantially square waves 22. These are applied to a condenserresistance combination 24, 25 to produce triangular waves 2 which are amplified by valve 26. Converting pulses of triangular form into pulses of varying duration determined by setting of fording control bias. The pulses 2 of triangular form are applied to the grid of valve 27, Fig. 6, which passes only that portion of the wave which exceeds the, particular amplitude level determined by the setting of the grid bias 28. Decapitated wave forms 29, thus produced in the plate circuit of valve 27, have their d.c. component restored by the diode 31 and resistor 32 and are applied to the grid of valve 30 which is biased by 33 to pass only the wave forms shown at 36. Biased diodes 37, 38 restore the D.C. component and produce control signals as at 41. In a modification, Fig. 6A (not shown), diode 31 is omitted and the valves 27, 30 have a common cathode impedance. The terminations of the control signals may be squared up by additional valve stages and filters comprising biased diodes, Figs. 7, 7A (not shown). Phase inverter. The shaped control signals are applied to the grid of a valve, Fig. 8 (not shown), pulses of opposite phase being taken from the anode and cathode circuits. These pulses are limited by pairs of diodes and then applied to the blanking-out amplifiers. Blanking-out and fading amplifier. The videosignals 65, Fig. 9, are applied to the grid of valve 63, the cathode circuit of which includes a biasing resistance 73 across which the blanking and fading-control signals 76, 79 may be applied by valves 71, 72 to control the gain of the amplifier 63. An additional valve 74 controlled by resistance 73 supplies a signal to the anode of valve 64 to balance out the blanking and fading control pulses which come through valve 63, as in Specification 493,289. To ensure a more complete balance of the fading control pulses, a resistance-condenser integrating circuit may be connected to the circuit of valves 63, 64, 74, Fig. 9A (not shown). Frequency doubling circuit. For certain fade-over patterns, a triangular wave of double the line frequency is necessary. This may be obtained from a triangular wave of line frequency by the circuit shown in Fig. 11, in which pulses of opposite phase derived from the anode and cathode circuits of valve 91 are rectified by diodes 94, 95 and add across the resistor 96 to give the double frequency wave 97. Specification 456,582 is referred to.