Patent GB-585613-A (GB)
Title: Improvements in super-regenerative receivers for electromagnetic waves
IPC: H03D11/02
Filed: 1944-09-15
Abstract: 585,613. Valve receiving circuits; pulse generating circuits; pulse modulation; radiolocation. STANDARD TELEPHONES & CABLES, Ltd., and EARP, C. W. Sept. 15, 1944, No. 17731. [Class 40 (v)] In a super-regenerative receiver for selecting a desired train of signal pulses from other pulses, the signals are fed to an oscillator which is normally quiescent, a train of sensitizing pulses being applied to the oscillator at the same repetition frequency as the desired signal pulses to allow initiation of oscillation by a signal pulse during the period in which the desired pulse may be received, means being provided for synchronizing the sensitizing pulses with the signal pulses. The circuit may be employed for the reception of pulses, modulated in phase or frequency, and may also be used on aircraft to give identification to a ground radiolocation station. By radiating pulses of different repetition frequency the ground station may identify a number of aircraft fitted with the apparatus adjusted to different repetition frequencies. The anode potential of valve 4, connected in a super-regenerative circuit, is normally insufficient to cause the valve to oscillate, signal pulses applied from aerial 30 being ineffective. Valve 1, connected as a transitron, oscillates at a frequency determined by the tuned circuit comprising condenser 10 and the primary 11 of an iron-cored transformer, the frequency being chosen near that of the desired pulse train. The output from valve 1 is fed to the grid of a squaring valve 2, the output of which is differentiated by condenser 19 and resistance 20 and applied to the grid of valve 3. Due to resistances 21, 23 the cathode of valve 3 is held sufficiently positive for no anode current to flow. The riegative-going pulses are without effect, but the positive pulses applied to the grid of valve 3 cause the valve to pass anode current and the cathode potential to rise, the condenser 22 discharging over resistance 21 between the pulses. The short positive sensitizing pulses from the cathode of valve 3 are applied over a coupling condenser to raise the anode potential of valve 4, oscillations being produced when a signal is received on the aerial 30. The grid condenser 25 charges rapidly negative and discharges slowly over a variable resistance 28, a charge remaining when the next sensitizing pulse is applied to the anode of valve 4, the grid potential continuing to rise as the anode potential falls, thus maintaining the valve 4 near the point of oscillation. When a signal pulse causes the valve 4 to oscillate the anode potential falls suddenly, feeding a negative pulse over the coupling condenser to the primary of transformer 34. A positive synchronizing pulse appears on the secondary of transformer 34 and is fed to the grid of a gating valve 5, the sensitizing pulses also being fed to the suppressor grid of the valve. The circuit is arranged for valve 5 to pass a maximum of anode current when a synchronizing pulse coincides with the peak of a sensitizing pulse, the valve normally being biassed beyond cut off due to resistances 36, 37. If the signal pulse is late relative to a sensitizing pulse, the synchronizing pulse on the grid of valve 5 appears after the sensitizing pulse has passed its maximum value and a correspondingly smaller anode current flows in valve 5. The pulses of' anode current pass through the secondary 12 of the iron cored transformer and vary the frequency of oscillation of valve 1. When no signal pulses are being received, valve 1 oscillates at a frequency corresponding to the maximum period between two signal pulses, and when a signal coinciding with the maximum of a sensitizing pulse is received valve 5 is arranged to shorten the,period of oscillation of valve 1 to the minimum spacing between two signal pulses. When receiving a pulse train, a state is rapidly reached when any increase or decrease in frequency of the signal pulses results in a corresponding change in the frequency of oscillation of valve 1. Rectified and amplified pulses may be obtained from the grid of valve 5 when the apparatus is operating as the receiver in a pulse communication system. If the signal pulses are time-phase modulated, the modulating signals may be obtained from the anode of valve 5 after passage through a low-pass filter. In a modification, the valve 5 is fed with D.C. pulses, which are effective during the period corresponding to the leading edge of the sensitizing pulse, valve 1 oscillating at a higher frequency which is decreased by the action of the D.C. pulses. Specification 509,820 is referred to.