A calculator for Butterworth and Chebyshev crystal ladder filter design, done as a Lotus 1-2-3 spreadsheet. This spreadsheet was created on Lotus 1-2-3 Release 4, but is a .WK1 file (and associated .FMT file The method used is from May 1982 QST, "A unified approach to the design of crystal ladder filters", by Wes Hayward, W7ZOI, p. 21
