Patent GB-693309-A (GB)
Title: Improvements relating to the synchronization of electric timebase circuits
Inventor: WILLIAMS FREDERIC CALLAND
IPC: H04N5/12
Filed: 1950-12-18
Abstract: 693,309. Automatic frequency and phase control systems. FERRANTI, Ltd. Dec. 17, 1951 [Dec. 18, 1950], No. 30736/50. Class 38 (iv). [Also in Group XXXVI] A time-base circuit, kept automatically in frequency and phase agreement with synchronizing pulses, comprises a sine-wave oscillator for locking the time base circuit and for providing a reference waveform of pulse sawtooth or other recurrent shape, and a discriminator for deriving, from the relative phase or coincidence of the reference waveform and the sync. pulses, a D.C. control signal which is applied to a frequency-determining saturablecore reactor in the tuned circuit of the sinewave oscillator. As shown in Fig. 1, the sinewave oscillator comprises a tube 10 with its anode coil 18 back-coupled to a tuned grid circuit consisting of a condenser 11 in parallel with a pair of coils 12, 14. Output is applied to the grid of a tube 20 at whose anode the waveform 26 is produced which is converted in a further tube 30 into positive-going pulses 36. These pulses provide a saw-tooth current in the coils of the time-base output circuit 35, and also are applied through a capacity 45 to the anode of a triode tube 41 to whose grid the sync. pulses 43 are fed. During coincidence of the two input pulses, anode current pulses occur which are smoothed by the circuit 49, 50 and provide a D.C. voltage at the junction of anode resistors 47, 48. Current varying with the phasing error is fed through the lead 51 to the coils 12, 14 in series thus varying the saturation of their core and adjusting the tuning of the oscillator in the corrective sense. Fig. 2 shows the arrangement of the coils 12, 14 on arms 60, 62 of the saturable core 64, on which the anode coils 18 are also wound to provide the back coupling. So far as the oscillations are concerned the coils 12, 14 are in parallel, being directly connected at one end and through a capacity 15 at the other. Consequently the path of the oscillatory flux is of high reluctance through the gapped centre leg 61. On the other hand, the direct current from lead 51 passes to earth through the coils 14, 12 in series and the flux resulting therefrom has a low reluctance path 60, 64, 62. The oscillator frequency is initially set approximately equal to the sync-pulse frequency by adjustment of the variable resistor 48. In the absence of sync pulses, the frequency of the oscillator 10 is maintained at one end of its range, and is swept towards the value appropriate to synchronism when the sync. pulses are applied. In a modified circuit, Fig. 3 (not shown), the output of the sine-wave oscillator is converted to a saw-tooth form and is applied to the outer control grid of a multi-grid tube, the sync. pulses being applied to the inner control grid. The output lead 51 for control of the frequency is taken from a variable tap on a resistor connected across the H.T. supply, the tap being connected through a resistor to the anode of the multi-grid valve. A resistor may replace the capacity 15 in the grid circuit 11 ... 14.