Patent GB-599611-A (GB)
Title: Improvements in or relating to frequency control apparatus
IPC: H01J25/00
Filed: 1944-12-23
Abstract: 599,611. Automatic tuning correction; velocity - modulated tubes. SPERRY GYROSCOPE CO., Inc. Sept. 13, 1944, No. 17537. Convention date, May 11, 1943. [Classes 39 (i) and 40 (v)] For automatically controlling the operating frequency of a cavity resonator device having thermally extensible tuning means, a periodically varying signal controls the energy source operating the tuning means, and the resulting periodic frequency variation is interrupted by means responsive to a predetermined relation between the operating frequency and a desired frequency condition of the device. The invention is described as applied inter alia to a pulse radar receiver, and in one embodiment, Fig. 2, the local oscillator is a reflection type velocitymodulation valve 16, the resonator 26 of which is tuned by a thermally expansible strut 32 surrounded by a heating coil 33. The heating current is supplied from the secondary of a transformer 51 in the anode circuit of a valve 47, the grid of which is fed with square-wave voltages, of a low frequency, from source 48. The heating current is controlled by applying D.C. voltages to the same grid from a sawtooth oscillator comprising the cold-cathode discharge tube 37, condenser 34 and discharge resistance 41 in parallel therewith. In the absence of any further control, the frequency generated by valve 16 is thus periodically varied over a range including that which produces the required intermediate frequency from the receiver mixer. Pulses of I.F. from the mixer are applied to a frequency discriminator and'produce D.C. pulses of a polarity dependent upon the direction of the error if and when the I.F. is incorrect. These pulses are fed to amplifier 52, the output from which is applied to the grid-controlled gas-discharge tube 53. The latter is biassed to cut-off but becomes conductive when positive pulses are applied, due to the intermediate frequency dropping below the desired value, and the anode 61 of tube 53 becomes less positive to restore some of the charge in condenser 34 which is discharging through resistance 41. The tube 53 is blocked by condenser 70 after each positive pulse ceases and the increments in charge of condenser 34 move the I.F. towards the desired value while preventing the tube 37 from operating to produce the frequency-scanning sawtooth voltages. In a modification of the control circuit, the oscillator strut heating coil 33, Fig. 8, is supplied from a low-frequency oscillator valve 72 whose anode voltage and output are controlled by valve 73, the grid bias of which is supplied from a potentiometer 74 connected across the saw-tooth oscillator condenser 34 of Fig. 2. Provision is also made in this circuit for a fine control of frequency by variation of the potential of the reflector electrode 28 of the oscillator 16. For this purpose the potentiometer 74 has a tapping 77 from which any voltage changes' are fed through condenser 78 to be superposed on the steady electrode voltage derived from potentiometer 83, The control voltages are delayed and smoothed by resistance 79 and condenser 81. The invention may also be used to control an oscillator so as to keep its frequency in a fixed relationship to that of a reference source of continuous waves. The outputs of the oscillator and reference source are applied to a mixer whose I.F. output is converted into a pulsed wave in a blocking amplifier controlled by a pulse generator. The resultant I.F. pulses are used to control the oscillator frequency as described above. Another type of oscillator which may be controlled by the circuits of Figs. 2 and 8 is shown in Fig. 9. The two coupled cavity resonators 84, 88 are controlled simultaneously by thermally-expansible struts 97, 98 and heater coils 99, 101 connected in series. The Specification as open to inspection under Sect. 91 comprises also a valve, the resonator frequencies of which are controlled by the variable magnetic attraction between pairs of electromagnet poles 107, 108, Fig. 10 (Cancelled), and 107<1>, 108<1> wound with series-connected coils 109, 111, 109<1>, 111<1>. Each pair of magnets is spaced apart at its lower end by a flat spring 113, 113<1> of magnetic material. This subject-matter does not appear in the Specification as accepted. Specifications 523,712 and 535,767 are referred to.