...under perpetual construction.
Here you can find the source code of the bpfilt program, for designing narrowband bandpass filters. You can choose between the equiripple (Tchebyscheff), maximally flat (Butterworth) and minimum loss (Cohn) types.
The output is a netlist in APLAC or Spice (OPUS Spice) format.
Download the bpfilt source code.
Here is a design example of a filter for the LF band, centered at 137.7 kHz, with several types of coupling and matching.
Here is another design example, comparing the Cohn, Tchebyscheff and Butterworth filter types.