620,478. Pulse discriminating circuits. LORD, A. V., and PYE, Ltd. July 14, 1945, No. 18054. [Class 40 (vi)] [Also in Group XL (b)] In an arrangement for separating frame and line synchronizing pulses in television and like systems the combined pulses are fed through a limiting device, which conducts only during the intervals between pulses, to a charge circuit which is charged up during the said intervals and which discharges by different amounts during the differing periods of the frame and line pulses, the charge circuit being connected to a second limiting device which conducts only during the frame synchronizing pulses due to the reduced potential of the charge circuit during the longer frame synchronizing pulses. The synchronizing pulses are separated from the picture signals in valve V1, which is biassed to conduct only during the synchronizing pulse periods. Line synchronizing pulses are derived from the output of V1 by means of the differentiating circuit C1, R1, the negative peaks of the waveform constituting the required pulses. The output of V1 is also fed to diode D1, which is so biassed by resistors R2, R3, R4, that it conducts only during the peaks of the potential waveform at the anode of V1, and the resistor R and the condenser C2 are of such value that C2 can be fully charged during the intervals between either the line or frame synchronizing pulses irrespective of the potential to which it discharges through R2. During the longer frame pulses FP the condenser discharges to a lower potential than during the shorter line pulses LP and a second diode D2, which is biassed by R5, R6, R7, to conduct at this lower potential, supplies the frame synchronizing separated from the line synchronizing pulses.
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