Patent GB-441793-A (GB)
Title: Improvements in or relating to electrical oscillation generators and control apparatus therefor
IPC: H03B5/18
Filed: 1934-10-04
Abstract: 441,793. Automatic control of oscillation frequency. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) Oct. 4, 1934, No. 28446. Convention date, Oct. 4, 1933. [Class 38 (iv)] [See also Groups XL and XXXVI] A push-pull short-wave valve oscillator MO has its frequency accurately regulated by a resonant circuit of the long-line type comprising U-shaped tube 2, 4, Figs. 1<b> and 2, one quarter wave length long, with its centre-point 74 connected to the valve cathodes and with symmetrically-disposed points 76, 78 connected to the grids. The electric length of the tube is adjusted by telescoping extensions 10, 12 at the free ends. Temperature variations in the long-line may be reduced by thermostatic control, by placing it in a refrigerating chamber, by burying it in the ground, or by circulating air or water through the inner tube. Hygroscopic material should be used to prevent water condensation on the tube. Temperature compensation may also be effected by a pipe containing oil and exposed in part to changes in room temperature and in part to changes in line temperature, the end of the pipe being closed by a " bellows " which adjusts condenser plates or the telescopic long-line extensions to maintain frequency constant. The main oscillator is kept in frequency agreement with a standard oscillator by a zero heat method which distinguishes between excursions above and below the standard and automatically corrects them. The standard source 122, Fig. 3, is coupled to the input circuits of two rectifiers 130, 132 through circuits one of which includes a phase shifter 134 to cause a relative adjustment of about 60‹ in phase. The main oscillator 135 feeds in the same phase to both rectifiers. The beats, which appear in the output circuits 150, 152 when there is a frequency shift, are displaced in phase the same amount as the phase shift given by the device 134. Which of the two has the leading phase is dependent on whether the oscillator 135 is giving too high or too low a frequency. These beats are applied to the grids of two valves 154, 156 which have a relay coil 116 differentially connected in their plate circuits. Owing to the self-biassing action of a grid leak and condenser 162 in the common cathode lead 170, the plate current of the valve whose grid receives the leading phase predominates over that of the other valve, operates its reversing-contact 118 to restore the frequency of the controlled oscillator 135 to normal. Meters 174, 176, 178 also provide visual indication of the amount and sense of the frequency error. The amount of frequency error required to set the restoring mechanism into action is dependent on the time constant of the elements 162. The width of the frequency band over which the device is self-restoring may be widened by further resistance-condenser combinations 166, 168, 170 with different time constants in the cathode lead to the plate or grid circuits. By suitable design of the transformers 150, 152, the amplitude of beat applied to the grids of valves 154, 156 may be negligibly small until the frequency error is more than a certain amount, say 250 cycles. The functions of the valves 154, 156 may be performed by the earlier valves 130, 132. The valves 154, 156 may be replaced by grid glow tubes, the grid receiving the earlier phase causing a discharge through that tube and a corresponding operation of the relay 116. A.C. supply is used for the plate circuits, Fig. 3a (not shown). An alternative valve circuit for operating the relay 116 comprises reciprocally-coupled valves. Bias for the valves is provided by rectifying the beat-frequency input, and the circuits are therefore immediately rendered inoperative during a period when either of the oscillators is idle, e.g. during keying, Fig. 3b (not shown). The relay 116 may serve to reverse a motor 114, Fig. 2, which by screw gear raises or lowers a capacity plate 112 to adjust the frequency of the long-line. Alternatively the motor may adjust in opposite directions a pair of plates 200, Fig. 6, relatively to the opposite sides of the line ; or the motor may vary a condenser or inductance in a closed resonant circuit. The relay 116 may be omitted, and the plate currents of the valves 154, 156 may operate an alarm or control a reversible motor directly. In the circuit shown in Fig. 4, the valves 154, 156 are reciprocally coupled by condensers 188, 190 and by coupled plate coils 192, 194 with the object of accentuating the difference between the plate currents whenever one of them begins to predorninate. In a further modification, Fig. 5 (not shown), the same effect is produced by coupling the plate coils 192, 194 to coils in the input grid circuits, or to coils in the circuits of auxiliary grids. The Specification as open to inspection under Sect. 91 states that the automatic frequency control is applicable to oscillators in general; and that the phase-indicating circuits may be used in audio-frequency apparatus, and in power equipment for synchronizing generators. Specification 352,621 is referred to, as an example of a suitable reciprocally-coupled valve circuit for operating the relay 116. This subject-matter does not appear in the Specification as accepted.