Analog filter design for improved performance in an atmosphericnoise environment

摘要

It is shown that several transitional low-pass characteristics canbe converted accurately to realizable bandpass crystal filters for thevery narrowband case (0.17% relative bandwidth and smaller). Ordinarydesign techniques such as Dishal's are applicable up to 5% relativebandwidth; but beyond that, up to about 50%, special techniques likebandwidth scaling and center frequency translation of a desirablelow-pass pole-zero cluster are required. Further modification of thebandpass cluster is simply performed. The proposed approach isapplicable to a modern high-performance superheterodyne radio receiverto meet several VLF/LF applications