Selectivity, a Simplified Mathematical Treatment

This paper gives a simple formula for finding the voltage gain of a resonant circuit at different frequencies in terms of that at resonance. Tables and curves are given in decibels below the resonant value so that calculations are quickly made. Means of converting the ordinary radio-frequency circuit into an equivalent simple resonant circuit are given so that a close approximation of its behaviour may be obtained, especially in cascaded circuits of diverse tuning. The criteria for maximum gain etc., are discussed by means of the equivalent circuit. A new expression for selectivity is proposed in terms of decibels below resonance. The principle of diverse tuning of cascading circuits to obtain band-pass effects is discussed.