Analog filter design for improved performance in an atmospheric noise environment

It is shown that several transitional low-pass characteristics can be converted accurately to realizable bandpass crystal filters for the very narrowband case (0.17% relative bandwidth and smaller). Ordinary design techniques such as Dishal´s are applicable up to 5% relative bandwidth; but beyond that, up to about 50%, special techniques like bandwidth scaling and center frequency translation of a desirable low-pass pole-zero cluster are required. Further modification of the bandpass cluster is simply performed. The proposed approach is applicable to a modern high-performance superheterodyne radio receiver to meet several VLF/LF applications