The Equivalent Selectivity of Transformer-Coupled Loop-Antenna Input Circuits

The over-all or equivalent selectivity of the simple transformer-coupled loop-antenna circuit is considered. From the analysis, design criteria are obtained. Graphs of equivalent circuit Q are so presented that intermediate design values can be determined by interpolation. Conclusions are that the net over-all circuit Q may be somewhat higher than that of the loop antenna for particular cases of elements with high Q values or for low values of transformer coupling. The magnitude of the over-all net Q is, in large measure, dependent on the Q values of the three elements in the circuit (loop, transformer primary, and transformer secondary). The relative changes in the input circuit selectivity with variation in the Q value of each circuit element, the influence of the transformer coupling, and the effect of the primary to loop-inductance ratio are discussed.