The direct measurement bandwidth

Traditional methods of bandwidth measurement are based on somewhat arbitrary specifications, for example´, the frequency difference between the high and low frequencies at which the single-tone response provides half the power corresponding to the frequency of maximum response. Other definitions of bandwidth or cut-off frequency are used in special cases whenever they seem appropriate. The lack of standardization in this matter creates confusion which is only now being resolved by the concept of equivalent bandwidth. A review of this concept is given to facilitate discussion of the measuring instruments described.