GB818781A - Improvements in or relating to automatic frequency controlling systems - Google Patents

Abstract

818,781. Automatic frequency and phase control systems. MARCONI'S WIRELESS TELEGRAPH CO. Ltd. July 29, 1957 [Nov. 20, 1956], No. 35406/56. Class 38 (4). An automatic frequency or phase control system is arranged to have rapid " pull-in " time when out of synchronism but slow rate of follow once synchronism is reached. As shown, a diode bridge is gated open by pulses applied at C, D from an oscillation source to be controlled in frequency and phase so that pulses of amplitude dependent on the instantaneous amplitude of a reference source A, B, e.g. mains frequency, passes to an integrating circuit. This first comprises a capacitor C1 in series with a resistance R4 shunted by a pair of oppositely-poled unilaterally conducting devices V1, V2 so biased that they are non-conducting when near synchronism between the oscillation sources is reached. The effective value of the series resistor R1 of the smoothing circuit R1, R3, C2, C3 is therefore large, giving a long time constant, but during out of synchronism the devices V1, V2 are conductive during most of the duty cycle giving R1 to normal effective value and a rapid time constant. The, resistor, R4 may alternatively be connected to the midpoint of the resistor of a parallel R-C network connected between the diodes V1, V2 so that a single source may bias both the diodes. The system may stabilize the frequency and phase of a television synchronizing pulse generator of frequency of twice the line frequency followed by frequency division down to frame frequency to derive the pulses applied at C, D.