41/40-meter RF filter

My initial experimentations with homebrew radio started with the 41-meter shortwave listening (SWL) band and the 40-meter amateur band. In order to improve my received signal quality, I decided to design and construct a bandpass filter to cover these two bands. I was inspired by articles such as Band-Pass Filters for HF Transceivers by Lew Gordon, K4VX. I made a simple PCB following the design in that article, although I made a sixth-order filter, rather than a fifth-order filter. I used the late Tony Fisher's LC filter design web page to determine the inductor and capacitor values for a Butterworth band-pass filter. I'll have to dig through my notes to see if I can find the exact parameters used. I'll post them when I find them. I did find the PCB pattern and the component values and toroid winding instructions. These are contained in the two Adobe PDFs at the bottom of this web page.

Below is a photo of the finished filter, with the cover remove to show the interesting bits. The circuit could certainly fit in a much smaller case, but the RadioShack Aluminum Project Enclosure (270-238) is still the best deal available in a small metal enclosure. The next thing cheaper is an Altoids tin. I still use this filter on occasion to listen 41-meter SWL, but it has been primarily replaced by my four-band filter.