Now that I'm getting better at passive filter analysis I wonder about techniques for filter design. Unfortunately, I keep coming to the conclusion that filter design comes from experience with filter analysis or the use of well known polynomials such as the butterworth and chebychev. Often this means going to a book of response graphs, choosing the desired response and following the procedure to denormalize the component values from tables. I'm presented with a front end filter to a 20m DC receiver (the one in the 2003 ARRL handbook). I've analyzed it every which way I can think of but I have no clue what technique the original designer used. I'd like to know so I can use it myself in future designs. Am I missing something?