An Automatic Digital Q-Meter: New Approach to the Digital Measurement of Magnification Factor

Few procedures, known so far, for the design of a digital Q-meter, were based on the ratio between the reactive and the nonreactive components of measured circuit elements or on the determination of the corresponding logarithmic decrement in that circuit. In the first procedure, the ratio of two voltages, proportional to the above mentioned components, has to be found and numerically displayed, when the same current passes through these components. This procedure is limited to relatively low frequencies and hence to small values of a Q-factor. In the second procedure, the number of damped oscillations in the circuit with the tested elements, which occur in the time interval between the initial amplitude of a suddenly injected signal and the damped amplitude eπ time smaller than the first one, corresponds to the numerical value of the Q-factor. The new procedure, presented in this paper, results in the numerical display of the Q-factor of an oscillatory circuit (or of its self-inductive element) at a relatively high resonant frequency. The procedure is based on the determination and numerical display of the ratio between the overvoltage, created by the resonance, and the high-frequency voltage injected in the oscillatory circuit. During the sweeping of the frequency-modulated injection signal around the proposed resonant frequency, the differentiation of the corresponding resonance curve is made; the passage of the differentiated signal through the zero value is marked by an appropriate comparator circuit.