Patent GB-654887-A (GB)
Title: Superregenerative receiver
IPC: H03D11/02
Filed: 1948-05-21
Abstract: 654,887. Super-regenerative receivers; frequency - modulation. HAZELTINE CORPORATION. May 21, 1948, No. 13837. Convention date, June 7, 1947. [Classes 40 (v) and 40 (vi)] A super-regenerative receiver operating in the saturation mode is stabilized against variations of H.T. supply voltage, input signal voltage or other circuit conditions by regulating the operation of the super-regenerator valve in dependence upon the average value of the current supplied to the valve from the H.T. source. In Fig. 3 an input tuned circuit 13 is connected to the control-grid of a valve 10 and is rendered oscillatory by a feed-back coil 17 in the cathode circuit. The quench voltage is applied to the grid from a conventional oscillator 22 and the modulation output is fed from the anode through an auxiliary. volume control 32 and a distortion correcting stage 29 to the output stages. It is explained that variations in H.T. supply voltage, carrier strength, circuit damping &c. vary the average oscillation build-up period and thus the selectivity and other operating characteristics of the receiver but since such variations are accompanied by a change of average anode current they may be prevented by providing a large cathode resistor 26. This resistor is byepassed by a capacitor 27 to modulation and higher frequencies and the steady bias it produces is offset by a voltage applied to the grid from the H.T. supply through a potentiometer 25, 28. A volume control potentiometer contact 21 when moved to the right decreases the output by shunting the output transformer and also by increasing the screen voltage. The increase in screen voltage causes the anode current to rise, producing a higher biassing voltage across the cathode resistor. A decrease of oscillation build-up time results and it is shown that this has the effect of reducing the modulation output voltage. The quench volt age amplitude may be limited by a diode circuit (Fig. 5, not shown) to produce a sharper knee where the negative conductance characteristic of the super-regenerative circuit reaches its maximum value. Self-quench operation may be brought about by suitably choosing the grid-biassing circuit constants (Fig. 6, not shown) in which case the cathode resistor by maintaining the average build-up time constant also maintains a constant average quench repetition frequency. In a modified circuit (Fig. 7) a saw-tooth quench wave (Figs. 8a and 8b) is generated by charging a capacitor 53 from the H.T. source and periodically discharging it through a valve 23 arranged as a blocking oscillator. This wave is passed through a limiter circuit biassed by the voltage (e1 - e0) developed across a small resistor 50, to conduct at the grid voltage increment corresponding to maximum desirable negative conductance of circuit. Changes of voltage across the cathode bias resistor 26 caused for example by an increase in carrier voltage alter the level on the saw-tooth curve at which the valve 10 starts conducting, for example from e0 (Fig. 8a) to e<SP>1</SP>0 (Fig. 8b). Thus although oscillation buildup starts later in the cycle it may be arranged that the saturation level is reached at the same point. Not only does this assure that the saturation mode of operation is obtained over a wide range of signal strength but also it allows a large value of percentage modulation of the carrier to be effectively handled. In a final embodiment, Fig. 9, a triode self-quench superregenerator 101 derives its H.T. supply from a capacitor 271 charged from a constant current source comprising battery B and either a large resistor 261 or a pentode valve 62. Any tendency for the valve current to increase due to a change in operating conditions of the receiver is offset by the resulting decrease in voltage across the capacitor caused by the increased discharging current. By adjusting the time constant of the grid blocking network 58, 28 towards a value producing a rapid oscillation build-up and a relatively long period of constant negative conductance, the frequency response characteristic may be arranged to have rectilinear sides suitable for the detection of frequency-modulated signals. Amplitude distortion is corrected in by the use of a valve circuit 29 (Fig. 3) in which the signal is applied to two control grids, so producing a square law characteristic. The precise shape of this characteristic is varied by adjusting potentiometer 31. Specifications 653,916 and 654,886 are referred to.