Patent GB-528310-A (GB)
Title: Improvements in or relating to thermionic valve circuits
IPC: H04N5/10
Filed: 1939-02-25
Abstract: 528,310. Television ; valve generating circuits; impedance networks. BLUMLEIN, A. D. Feb. 25, 1939, No. 6266. [Classes 40 (iii) and 40 (v)] Delay networks with mismatched terminations producing reflection are used for producing timed impulses or for separating long and short impulses, e.g. line and frame synchronizing impulses. The network may be open-circuited or short-circuited so that the reflected impulses are of the same or opposite polarity. Producing impulses of predetermined duration from sawtoothwaves, or from impulses of longer duration, or at timed intervals. The network 4, Fig. 1, is short-circuited at 10 and terminated at its input end by an impedance 1, 2, 3 equal to the characteristic impedance of the network. Pulses, produced or repeated by valve 1, reaching the tapping point 5 render the valve 7 conductive, and the reflected pulses of opposite polarity render it non-conductive. The duration of the pulses at the anode of valve 7 is thus equal to twice the time taken by the pulse to travel from 5 to 10. The valve 7 may be replaced by a pair of valves in push-pull, as in Specification 482,740. Two consecutive pulses may be generated from a single input pulse by the arrangement shown in Fig. 2, in which the valves 14, 15 are so biased that when one is conducting the other is not. The initial pulse reaching the tapping 16 renders the valve 14 conducting until the pulse reaches tapping 17 and makes valve 15 conducting and valve 14 non-conducting. After an interval during which the pulse travels to 18 and back to 17, the valve 15 is rendered non- conducting and the valve 14 conducting until the pulse reaches 16 and renders 14 non-conduct. ing. The output of the double-frequency pulses may be obtained from either 14 or 15, their duration and the interval between them being determined by the position of the tappings 16, 17. A circuit similar to that shown in Fig. 1 may be used for producing (for A.V.C. or D.C. insertion) a pulse of, say, 4 microseconds beginning slightly after and ending slightly before an observation pulse of 5 microseconds following the line synchronizing pulse, Fig. 3 (not shown). Other similar applications are described. Separating vision, line and frame synchronizing impulses. The network is open-circuited so that the reflected impulse is of the same polarity as the initial pulse, and the delay caused by the network is greater than the duration of the line pulse but less than that of the frame pulse ; the reflected frame pulse reinforces the initial pulse so that the line and frame pulses may be separated by an amplitude filter. In the circuit shown in Fig. 4, vision signals are taken off by lead 31 from a valve 29 of the cathode follower type, the line synchronizing pulses are separated by valve 32, the cathode of which is connected by a self-biasing resistance-capacity combination 33, 34 to the cathode of valve 29 and the frame synchronizing pulses are derived from a valve 37 connected to the input end of the delay network so as to be influenced by the reflected overlapping frame pulses. During synchronizing signals, the valve 32 absorbs current which would normally flow to valve 29, thus increasing the current change due to synchronizing signals in valve 29 and producing large signals across the delay network. The delay in the derivation of the frame pulse is useful in interlaced scanning. Impedance networks. The coils of adjacent sections may be coupled, and m-derived sections may adjoin the terminations. As the delay is not constant for frequencies approaching the cut-off, the first coil or coils may be shunted with high resistance to attenuate the high frequencies. Specifications 422,906, 449,242, 458,585, 491,728, 496,119, 514,065, 514,271 also are referred to. Reference has been directed by the Comptroller to Specifications 531,712 and 538,553.