Patent GB-537375-A (GB)
Title: Improvements in or relating to synchronising signal generators
IPC: H04N5/06
Filed: 1939-11-30
Abstract: 537,375. Television ; thermionic valve circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Nov. 30, 1939, No. 31192. Convention date, Nov. 30, 1938. [Classes 40 (iii) and 40 (v)] The television synchronizing signal o, Fig. 2, comprising line frequency impulses followed by preparatory impulses at double linefrequency in turn followed by slotted framing impulses having slots at double line-frequency, is produced by generating by a common generator a continuous train of half-width impulses at double line-frequency, removing alternate pulses from the region of this train where linefrequency impulses are required by means of impulses occurring at linefrequency and derived from the common generator, widening the remaining pulses in that region by adding to their back edges pulses occurring at line-frequency and also derived from the common generator, adding to the back edges of the halfwidth double line-frequency pulses in the region where slotted framing impulses are required comparativelywide impulses occurring at double line-frequency and derived from the common generator, and so delaying the generated and derived impulses and adding the produced line-frequency impulses and the produced slotted framing-frequency that the front edges of the generated impulses provide the front edges of the line-frequency impulses of the framing impulses and of the constituent parts of the framing impulses separating the slots. In the circuit arrangement shown in Fig. 1, sine waves at double line-frequency are produced by a master oscillator 1 which receives its power from 60 cycle mains through a phase shifter 9. The sine waves are converted into rectangular impulses by a limiter or clipper circuit 7, and then. divided into linefrequency pulses by a curcuit 2 and into frame frequency impulses (=mains frequency) by a threestage circuit 3, 4, 6, the final stage 6 being locked to the power mains by a circuit 8. The video synchronizing train of pulses o, Fig. 2. is obtained with the circuits of Fig. 1 by the production and superimposition of four sets of impulses d, h, j, m as follows : The train d of half-width pulses at.double line-frequency is obtained from the common source 7 through a delay device, a multivibrator 11 which adjusts the width of the pulses, and a limiter circuit 12. The impulse train h for removing alternate half-width pulses is obtained from the common source 7 through a divider 2, a multivibrator 16 and a limiter-mixer circuit 17, 21, the pulses of this train not wanted during the framing period being removed in the mixer 17 by 60-cycle impulses obtained from the last divider stage 6 through a multivibrator 18 and a limiter 19. The impulse train j serving for doubling the width of the pulses of the'train d is obtained from divider 2 through a delay circuit, a multivibrator 22, a limiter-mixer 23 and a limiter 24, the pulses not wanted during the framing period being removed by an impulse train f obtained from divider 6 through multivibrator 18 and limiter 19. The impulse train m for producing the slotted framing-pulses is obtained from the common source 7 through a delay circuit, a multivibrator 31, a limiter-mixer 29 and a limiter 32 in conjunction with a 60-cycle frequency from the divider 6 through a multivibrator 26, a limiter-mixer 27 and a multivibrator 28 in the following manner : The chain of devices 7 ... 31, produces the pulse train k and a similar train of opposite polarity y; the multivibrator 26 energized from the divider 6 produces the impulse train g; the impulse train g is passed through a differentiating circuit comprising a small coupling capacity whereby a pulse train z is produced ; the pulse trains y and z are added to produce a pulse train r; this is clipped to produce a pulse train x; the leading edge of the pulse train x triggers off the multivibrator 28 to produce the pulse train l; and the pulse trains I and. k are added to produce the pulse train m. The pulse trains d, h, j, m are added up in a mixing circuit 13 to produce a pulse train n, and this is clipped at the levels indicated by the dotted lines shown in Fig. 2 to produce the final train o. The circuit arrangement shown in Fig. 1, in addition to producing the video synchronizing train o, produces also video blanking signal train a, horizontal iconoscope synchronizing train p,, vertical iconoscope synchronizing train c and iconoscope blanking signal train b. The details of the circuits indicated by the block diagrams of Fig. 1 are described with reference to Figs. 3a, 3b, 3c, 3d (not shown). The Specification as open to inspection under Sect. 91 describes also two other methods for production of the video synchronizing signal. In one, the pulses of the primary train serving to produce the others have the whole width of the desired line pulses and occur at double line-frequency ; in the other, the primary pulses at double line-frequency are wide and a few of them are utilized to form the slotted framing pulses. This subject-matter does not appear in the Specification as accepted.