The super-regenerative detector: an analytical and experimental investigation

Abstract

On the basis of an exponential build-up of oscillations in its grid circuit, the super-regenerative phenomenon is analysed and a general expression for the output at modulation frequency is obtained. This expression is examined term by term and reveals the mechanism of (a) high amplification, (b) self-a.v.c. action, (c) excessive distortion of the modulation frequency at modulation depths in excess of 50%. All these properties are quite characteristic of the super-regenerative detector in practical operation.Histograms illustrate the distortion effect in terms of modulation depth. Various oscillograms verify the mathematical results, particularly in regard to the law of build-up of oscillations as a function of the amplitude of the applied signal.The dependence of radio-frequency selectivity and modulation-frequency gain upon the quenching frequency is shown in the analysis and verified by measurements. It is shown that an optimum quenching frequency exists for maximum gain at the modulation frequency. If this optimum frequency is slightly exceeded, the noise background may be removed without severe reduction of gain.The ability of the super-regenerative detector to discriminate agamst impulsive radio-frequency interference (e.g. motor-vehicle igmtion interference) is analysed briefly. The reception of frequency-modulated signals is also discussed briefly.