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    Improvements to television transmitters
    22.
    发明专利
    Improvements to television transmitters 未知

    公开(公告)号：GB794348A

    公开(公告)日：1958-04-30

    申请号：GB212855

    申请日：1955-01-24

    Applicant: SOC NOUVELLE OUTIL RBV RADIO

    IPC: H04N5/18 ,  H04N5/38 ,  H04N5/40

    Abstract: 794,348. Television. SOC. NOUVELLE DE L'OUTILLAGE R.B.V. ET DE LA RADIOINDUSTRIE. Jan. 24, 1955 [Jan. 23, 1954], No. 2128/55. Class 40 (3). In a negative feedback loop for stabilizing the black level in a radiated television signal, the radiated signal is rectified at 22 and applied to a first gate V4A which is rendered conducting during a period extending over the black-level back porch so as to pass a current proportional to the actual black level radiated. A second gate V4B, connected in parallel with the first at the anode, conducts at a level corresponding to the correct black level and is rendered non- conducting during the black-level porch. The commoned anodes produce therefore output pulses whenever the current levels in the two gates differ and these pulses are applied through stages V5 and V6 to control the level in a D.C. restoration circuit which functions to clamp the video signal applied to modulate the transmitter. The D.C. restoration circuit may be of the type described in U.S.A. Specification 2,299,945. The switching of gates V4A, V4B is effected by a trigger circuit V1A, V1B which is triggered on the rear edge of the line synchronizing pulse so as to produce an output pulse during the back porch interval. The pulse is applied via phase inverter V2 directly to the grid of gate V4B and via stage V3 to the cathode of gate V4A. The pulses employed to actuate the D.C. restoration circuit are of shorter duration than switching pulses.

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