GB614942A - Improvements in or relating to methods of and means for producing modulating sequels for television transmitters - Google Patents

Abstract

614,942. Television. RADIO-INDUSTRIE SOC. ANON. May 22, 1946, No. 15500. Convention date, May 23, 1945. [Class 40 (iii)] In an arrangement for inserting synchronizing pulses into a television signal, means are provided for ensuring stability of the datum level portions (i.e. pedestals) to which the synchronizing pulses are added. A television signal V, Figs. 1 and 7, having a maximum level B131 representing white and a black level NN<1> is interrupted at a, b for insertion of synchronizing signals, such as pulse S (Fig. 3). To ensure stability of the level a, b at which these pulses are inserted, i.e. the black level NN<1> representing a modulation depth of approximately 30 per cent of the full modulation BB<1>, a locally generated auxiliary pulse series S1 having a repetition rate equal to that of the synchronizing signals to be inserted and an amplitude at least as great as maximum white, is inserted in the gap a, b giving a resultant such as the signal shown in Fig. 5. This signal is then fed to a limiter valve E, Fig. 8, which produces an output waveform V, Fig. 6, in which the stability of levels a, b and a1, b1, defining the pulse S<1>1, Figs. 6 and 8, is determined by the operational characteristic of the limiter E. 'An additional pulse series S<2>1 (pulse series S1 reversed in phase) is then applied to the limiter output to effect cancellation of the pulse S<1>1 and thus to produce a gap having a stable level a, b on which is superimposed the desired synchronizing pulse S1, Fig. 3.