An Examination of Selectivity

A review of the literature on selectivity including the important recent contributions shows the necessity for coördination of the results and clarification of the definitions. The present selectivity requirements are developed and a simple mathematical treatment is expanded to meet them. The criterion for uniform ability to reject undesired signals, for both condenser and inductance tuning, results from this calculation. The relation of the selectivity curve, as now taken and presented, to the actual performance of the receiver is discussed, and the central portion is compared mathematically with the fidelity characteristic. Possible improvements in the definition, method of measurement, and presentation of data, are suggested.