GB630871A - Improvements in oscillation generator systems - Google Patents

Abstract

630,871. Automatic frequency-control systems. FRANCE, H. G. DE. Aug. 29, 1946, Nos. 25978 and 25979. Convention dates, March 12, 1941, and July 5, 1941. [Class 38 (iv)] [Also in Group XL (c)] The line frequency generator of a television receiver is maintained constant with respect to the supply frequency by dividing down in a series of relaxation oscillators and compounding the frame frequency pulses and the supply to produce a potential for controlling each oscillator. Fig. 1 shows an arrangement in which a hard valve saw-tooth generator I of the Puckle type produces a saw-tooth of line frequency which synchronizes through a valve 6 the first generator II of a series of similar generators dividing down to frame frequency. The frequencies of the system can be adjusted so that the frame frequency is approximately that of the mains by adjusting potentiometer 7 controlling the screen potential of constant current pentodes 2, 2<1>. The system is locked .on to the mains by adding frame frequency pulses to a supply frequency wave in a device 8 to produce a wave which is rectified to produce a bias proportional to the phase difference between the wave and the pulses by circuit 10, 11 and is then applied to the control grids of the constant current pentodes 2, 2<1>. The operation of the divider chain is checked by connecting the outputs of successive stages to the X and Y-plates of a C.R. tube to produce a trace analagous to Lissajons, Fig. 6 (not shown). Thyratron generators may replace the hard valve generators, Figs. 7 and 8 (not shown), synchronizing pulses for successive stages being derived from resistors in the' cathode leads of the previous valve in these embodiments.