Measurements on intermediate-frequency transformers

A simple method for the testing of double-tuned I.F. transformers with the aid of a Q-meter or any other instrument capable of measuring R.F. resistance is shown. The resonant transfer impedance of a pair of coupled circuits is expressed in a form which is independent of the nature of the coupling reactance. Charts are presented which enable a rapid determination of the transfer impedance of the transformer, with or without resistive loading, to be made from three readings of the Q-meter. If the tuning capacities are known, these readings also are sufficient to determine the frequency response curve of the transformer with the aid of published generalized response curves. Simple formulÿ for the bandwidth at ¿60 db. of composite systems containing single and double-tuned circuits of different dynamic resistances and coupling have been developed.