Patent GB-535331-A (GB)
Title: Improvements in synchronizing systems and methods
IPC: H04N5/12
Filed: 1939-06-29
Abstract: 535,331. Valve generating circuits ; television. PHILCO RADIO & TELEVISION CORPORATION. June 29, 1939, No. 18965. Convention date, Aug. 12, 1938. [Classes 40 (iii) and 40 (v)] In television and other synchronizing systems in which synchronizing signals control the production of pulses, e.g. by blocking oscillators or condenserrelaxation generators, undesired signals are prevented from affecting the production of pulses by utilizing a modification of the operating conditions of the circuit, occasioned by the forming of a pulse, to render the circuit unresponsive to further signals during the " active period " of the pulse forming means. The term active period" means e.g. the abrupt stroke period of a relaxation generator or the pulse-forming period of a blocking oscillator, and may include several synchronizing pulses. The circuit may be rendered unresponsive during such periods by feeding back a potential to block or saturate a transfer valve or amplifier arranged between the source of synchronizing signals and the generator or oscillator. The synchronizing signal may itself be shortened by this feed back. In Fig. 6, image synchronizing signals are repeated by transfer valve V3 and phase-reversing valve V4 to a blocking oscillator V5, the pulses from which trip a valve V6 to discharge a relaxation condenser. A resistance 7 in the cathode circuit of V6 is connected over condenser 9 to the cathode of V3, thereby blocking this valve during the discharge period of the condenser, to prevent the passage of line synchronizing and extraneous signals as well as the latter portion of each image synchronizing signal. The blocking potential may be derived from the anode of the blocking oscillator V5, Fig. 10 (not shown), or from a resistance 13, Fig. 11, in the cathode circuits of both valves V5, V6, in which case valve V4 is omitted and the anode of V3 connected direct to the anode of V5. In a modification of Fig. 11, the blocking potential is derived from a resistance in the plate circuit of the blocking oscillator and applied to a resistance in the suppressor grid lead of valve V3, Fig. 12 (not shown). In another arrangement, the synchronizing signals are applied to the gas discharge tube of a relaxation condenser, the voltage from which is applied to the control grid of a high-resistance amplifier feeding the deflecting coils of the cathode ray tube, Fig. 13 (not shown), the blocking potential being derived from a resistance-capacity circuit in shunt with the deflecting coils. Instead of controlling a transfer valve or amplifier preceding the generator by a separate connection, the anode of the transfer valve may be connected directly to the anode of the blocking oscillator, so that during the active period the fall of potential on the anode of the oscillator is directly communicated to the anode of the transfer valve which is thus rendered ineffective. The image and line synchronizing signals may be more effectively separated in a somewhat similar manner by using a blocking potential derived from the image synchronizing circuit to prevent image synchronizing signals from entering the line synchronizing circuit and vice-versa, Fig. 15 (not shown). Specifications 477,038 and 489,102 are referred to.